Safe Sleep for Babies: Mattresses, Sleeping Bags and Room Temperature

Few things feel as important in the first year as getting your baby's sleep space right. The good news is that the official UK advice is clear and consistent, and most of it costs nothing: back to sleep, a clear cot, the right room temperature and a firm, flat mattress. This guide pulls together what The Lullaby Trust and the NHS say, and explains what to look for when you buy a mattress, a baby sleeping bag or a monitor. It is not medical advice: if you have any worries about your baby's health or sleep, speak to your health visitor, GP or NHS 111.

The basics that matter most

Before any product, these are the habits both the NHS and The Lullaby Trust put first. The Lullaby Trust says to follow its safer sleep advice until your baby is 12 months old (adjusted for babies born prematurely or at a low birthweight).

• On their back, every sleep. Day and night, including naps.
• Feet to foot. Place your baby with their feet at the foot of the cot or Moses basket so they cannot wriggle down under covers.
• Same room. The NHS advises a separate cot or Moses basket in the same room as you for every sleep for at least the first six months.
• A clear cot. No pillows, duvets, cot bumpers, loose blankets or soft toys – anything that could cover your baby's face and head.
• Never on a sofa or armchair. The NHS lists these as places to avoid for sleep, as well as smoke exposure during pregnancy and after birth.

A firm, flat mattress that fits

The Lullaby Trust's mattress and bedding guidance describes the safest mattress as firm, flat and protected by a waterproof cover, with no raised or cushioned edges or sides. It should fit your cot or basket snugly, with no gaps between the mattress and the frame.

Check the size before you buy

Cot and cot bed sizes are not the same everywhere, and many products sold online are made for other markets. Measure the inside of your cot base and compare it with the mattress dimensions in centimetres. A mattress that leaves a gap at the sides or ends is not a good fit, however well made it is. The Trust also names the relevant British Standards for mattresses (BS 7177:2008 and BS EN 16890:2017), which are useful to look for on the label.

Second-hand mattresses

If you reuse a mattress, check that it has no rips or tears, is firm and flat with no sagging, has a fully waterproof cover and carries a fire-resistance label.

Products to leave out

The Lullaby Trust advises against weighted swaddles, weighted blankets and weighted sleeping bags, as well as sheepskins, cot bumpers, and sleep pods or nests. Sleeping babies should not lie on, or have anything soft around, their heads.

You can browse cots, mattresses and sleep accessories in our nursery range.

Baby sleeping bags and tog ratings

A well-fitting baby sleeping bag is a popular alternative to sheets and blankets because it cannot be kicked off or pulled over the face. A few points from The Lullaby Trust's advice on dressing your baby for sleep:

• Fit by weight, not age. Most sleeping bags are sized by your baby's weight, and many are designed for babies from around 4kg. It should fit well at the neck and arm holes so your baby cannot slip down inside.
• No blankets on top. If your baby feels cold, add a layer of clothing or choose a higher-tog bag instead.
• Togs do not simply add up. Air trapped between layers changes the warmth, so two 1.0 tog bags do not equal a 2.0 tog bag.
• Follow the maker's chart. The Trust deliberately does not give tog numbers for each temperature, because every product uses different materials. Use the manufacturer's own room-temperature and clothing guide for the bag you buy.

The British Standard for baby sleep bags is BS EN 16781:2018. We stock sleeping bags and swaddles in a range of tog ratings in baby care; check the listing for the tog, weight range and the maker's temperature guide before you choose.

Room temperature and avoiding overheating

Both the NHS and The Lullaby Trust recommend a room temperature of 16–20°C for a sleeping baby. In a UK winter that often means turning the bedroom radiator down rather than up. A simple room thermometer takes the guesswork out of it.

• Check the chest or back of the neck. Hands and feet are usually cooler, which is normal. If your baby's skin feels hot or sweaty, remove a layer.
• No hats indoors. Babies lose heat through their heads, so a hat can make them too warm.
• Keep heat sources away. The NHS advises against hot water bottles and electric blankets, and against placing the cot next to a radiator, heater or fire, or in direct sunlight.
• Don't bundle up an unwell baby. Dress them for the room, not more than usual, and contact your GP or NHS 111 if you're worried about a fever.

Swaddling: if you choose to

Swaddling is a personal choice, and The Lullaby Trust's swaddling guidance sets out how to do it more safely:

1. Always put a swaddled baby down on their back.
2. Use thin, lightweight material such as muslin, keep clothing underneath minimal and leave the head uncovered.
3. Swaddle securely but leave room for the hips to move, and never wrap above the shoulders.
4. Keep the room at 16–20°C and check your baby is not getting too hot.
5. Stop swaddling with the arms inside as soon as your baby shows signs of rolling.

The Trust says not to swaddle when bed-sharing or when your baby has an infection or a fever.

Baby monitors: useful, but not a safety device for SIDS

The Lullaby Trust's baby monitor page is clear that there is no evidence monitors help prevent sudden infant death syndrome. Audio and video monitors are about convenience and reassurance; they do not replace the safer sleep basics above.

• Movement monitors sound an alarm if no movement is detected for a set time (usually around 20 seconds). If you want one, the Trust suggests choosing a product classed as a medical device and carrying a CE or UKCA mark.
• Wires and tubes. For skin-contact monitors with tubes, the Trust recommends stopping at six months or once your baby can roll, reach and grasp.
• Co-sleeping. Movement monitors will not work reliably when you share a bed, as they pick up your own breathing and movement.
• Placement. Follow the manufacturer's instructions and keep the camera and every cable well out of reach of the cot.
• Power. Many monitors are international versions. Check that the mains adapter is rated 100–240V (or 230V) and has, or is safe to use with, a UK plug. Never plug a 110–120V-only adapter into a UK socket.

Quick safe sleep checklist

• Back to sleep, feet to foot, in your room for at least six months.
• Firm, flat, waterproof mattress that fits the cot with no gaps.
• Clear cot: no pillows, duvets, bumpers, soft toys, pods, nests or weighted products.
• Sleeping bag sized by weight, with the tog chosen from the maker's guide; nothing on top.
• Room at 16–20°C, no hat indoors, cot away from radiators.
• Monitor adapter rated 100–240V with a UK plug, cables out of reach.

Stocking up on the rest of the essentials? Our UK nappy size guide explains how to pick the right size, and you'll find everyday items across our baby and kids department.

Frequently asked questions

What room temperature is recommended for a sleeping baby?

The NHS and The Lullaby Trust recommend a room temperature of 16–20°C. A simple room thermometer helps you check, and you can feel your baby's chest or the back of their neck to see if they are too hot.

What tog sleeping bag should my baby use?

The Lullaby Trust does not give tog numbers for each temperature because products are made from different materials. Follow the manufacturer's room-temperature and clothing chart for the bag, and never add blankets on top.

Is it safe to swaddle my baby?

If you choose to swaddle, use thin material, keep your baby on their back, leave room for the hips and don't wrap above the shoulders. Stop swaddling with the arms inside once your baby shows signs of rolling, and don't swaddle when bed-sharing or if your baby has an infection or fever.

Do baby monitors reduce the risk of SIDS?

The Lullaby Trust says there is no evidence that baby monitors help prevent SIDS. They can offer convenience and reassurance, but they do not replace safer sleep advice.

What makes a cot mattress safe?

The Lullaby Trust describes the safest mattress as firm, flat and protected by a waterproof cover, with no raised or cushioned edges. It should fit the cot with no gaps between the mattress and the frame.