A 2027 Checklist for Choosing the Right Cot Bed Mattress Thickness
Disclaimer: This guide is for general information only and should be read alongside the instructions supplied with your cot, cot bed and mattress. Always follow the manufacturer’s guidance on mattress size, maximum mattress depth and cot-base height. For current safer-sleep advice, refer to the NHS and The Lullaby Trust, which recommend a firm, flat, waterproof mattress that fits the cot correctly, with babies placed on their back in a clear sleep space. If you have any concerns about your baby’s sleep or safety, speak to a healthcare professional.
The right thickness for a cot bed mattress is one that gives your baby a firm, flat surface, fits the cot with no gaps at the edges, and sits low enough that the sides of the cot still do their job. Our Hybrid® Cot Bed Mattress is 10cm deep and is built to conform with BS EN 16890, the safety standard for cot mattresses. This checklist explains why thickness matters, what else to look for, and how to be confident in your choice.
Why Thickness Matters For Babies
A cot mattress has a different job from an adult one. Babies need to lie flat and straight, because their bones are still soft, and overly plush, soft or cushioned mattresses can increase the risk of suffocation. A firm, flat mattress is the safest choice for babies between 0 and 12 months.
Thickness plays into that in two ways. A mattress that's too thin can't be firm and supportive across its whole surface. A mattress that's too thick raises your baby higher in the cot, which reduces the height of the sides once they start to pull themselves up.
The Checklist
Run through these points before you choose.
- Depth. Look for a depth that gives firm, flat support without raising your baby too high in the cot. Ours is 10cm.
- Safety standard. Check that the mattress conforms with BS EN 16890, and that it has all the external safety features that standard requires.
- Fit. Measure the inside of your cot bed and choose a mattress that fits snugly. With our Cot Bed Mattress, the gap between the mattress and any side or end of the cot must not exceed 30mm, and you should never use more than one mattress in the cot.
- Firmness by age. Newborns need a firm, flat side. Toddlers need more responsive, cushioned support. A double-sided mattress covers both.
- Washable cover. Look for a cover that zips off for machine washing, and a water-resistant inner layer beneath it.
- Materials. Choose hypoallergenic materials that are free from harmful chemicals and common irritants.
- Edge support. Firmer springs around the edges help prevent dipping when your toddler stands or plays.
- Storage. Keep the mattress flat until it's needed, and store it flat.
How The Hybrid® Cot Bed Mattress Measures Up
Our cot bed mattress was designed around that list.
- 10cm deep, with all the external safety features required to conform with BS EN 16890
- Double-sided. The Baby side is firm and flat for newborns and babies up to 12 months. Flip it at one year to the Toddler side, which has our Aerocoil® microsprings for cushioned, edge-to-edge support. Firmer and Softer labels on each side tell you which way round to have it
- 648 conical pocketed Aerocoil® springs, made with high carbon steel and manufactured in Leeds, so the Toddler side responds to your child's every movement
- A border of firmer springs around the edges, to prevent dipping when your child stands or plays
- Simba Renew™ comfort layers, heat-treated to the correct firmness and density for each side
- A water-resistant inner cover and a soft, breathable, knitted outer cover that removes easily for machine washing
- CertiPUR® verified materials, free from harmful chemicals
It's suitable from birth to around three years old and above, so one mattress covers the whole cot bed stage.
Checking the Fit In Your Cot
Measure the inside length and width of your cot bed at the mattress base. Compare those with the mattress dimensions on the product page. The mattress should fit snugly, with no gap that a small hand or foot could slip into.
Once it's in place, check the height of the cot sides above the top of the mattress, with the base at its lowest setting. If your cot has an adjustable base, lower it as soon as your baby starts to sit up or pull themselves up.
After the Cot Bed
When your child is ready for a full-size bed, thickness matters again, this time for the bed frame. If they're moving into a bunk or cabin bed, safety regulations limit the mattress depth, which is why our Hybrid® Kids Mattress is a UK single with a shallower 16cm depth. Bunk and cabin beds aren't suitable for children under three. For a standard single frame, any of our high tech mattresses will work in a single size.
Looking After A Cot Bed Mattress
- Use a fitted sheet, and wash the outer cover whenever it needs it.
- Wipe the water-resistant inner cover with a damp cloth if anything gets through.
- Keep the mattress flat at all times, including when it's stored.
- Follow the care label for washing temperatures.
FAQs
Yes. A cot mattress needs to be firm and flat, and 10cm gives that support while keeping your baby low in the cot so the sides stay effective. Our mattress conforms with BS EN 16890 at this depth.
A cot bed is larger than a standard cot and converts into a toddler bed, so its mattress is larger too. Always measure your cot or cot bed before you buy, and choose the mattress that matches those dimensions.
No. Newborns and babies up to 12 months need the firmer Baby side. Flip the mattress to the Toddler side when your child turns one.
The Simba cot bed mattress has a 2-year guarantee; the standard 200-night trial for Simba mattresses does not apply to the cot bed mattress. Please check the product terms on our website for the full guarantee details.
It's designed to be kept flat, so please store it flat until it's needed. You'll find delivery details on the product page, and accessories ordered before 1pm arrive the next working day to most UK postcodes.
