The single most-asked question we get about mattress toppers is how thick they should be. There's no universal right answer – it depends on your sleep position, your current mattress, and what you're trying to fix. Here's the practical breakdown.

The short answer

For most UK buyers, 4 inches (10 cm) is the sweet spot. Enough to genuinely change how the bed feels, not so much that you feel like you're sinking.

Match thickness to your sleep position

Side sleepers

Side sleeping puts pressure on the shoulders and hips. A thicker topper (4 inches) cushions those points and reduces the pressure-point pain that wakes side sleepers up.

Going below 3 inches as a side sleeper rarely helps – the shoulder still bottoms out onto the firm mattress beneath.

Back sleepers

Back sleepers need lumbar support more than cushioning. A medium topper (3–4 inches) that holds its shape works better than a deep, plush one that lets the lower back sink.

Microfibre toppers in this thickness range are usually the right call for back sleepers.

Stomach sleepers

Stomach sleeping is hard on the lower back already. Adding a thick topper makes it worse – the abdomen sinks, the spine arches. Stick to 2 inches max.

Combination sleepers

If you switch positions through the night, 3–4 inches gives you something for each. Not perfect for any one position, but workable for all three.

Match thickness to your current mattress

Newish mattress, just want a softer feel

2–3 inches is plenty. You're adding a layer, not rebuilding the bed.

Older mattress that's gone firm

4 inches. Substantial enough to mask the firmness without committing to a new mattress.

Sagging mattress

A topper won't fix a sagging mattress. The topper just sits on top of the dip and you'll still feel it through. If you can see your mattress sagging in the middle, replace the mattress – don't add a topper.

New, very firm mattress (e.g., orthopaedic)

4–5 inches if you're trying to soften it. Anything less and the firmness still wins.

Don't forget the depth fit

UK mattresses with a topper layer can easily exceed 30–40 cm of total depth, which means you also need:

• A topper with strong elastic straps that fit your mattress depth (the SAIMAZ 4-inch microfibre topper fits up to 40 cm)
• An extra-deep fitted sheet with a 30–40 cm pocket to go over the top – a standard 25 cm fitted sheet won't reach. See our 40 cm extra deep fitted sheet.

What about material thickness vs density?

Thickness isn't the only thing that matters. A 2-inch high-density topper can feel firmer than a 4-inch low-density one. For microfibre toppers, look at the GSM (grams per square metre) of the filling – 1000 GSM and above is genuinely supportive; lighter than that is more like a quilted protector with cushioning, not a real topper.

The SAIMAZ topper uses 1200 GSM microfibre filling – dense enough to support, breathable so it doesn't trap heat the way memory foam can.

UK sizes and what to check

All SAIMAZ mattress toppers come in five UK sizes:

• Single (90 × 190 cm)
• Small Double (122 × 190 cm)
• Double (137 × 190 cm)
• King (152 × 200 cm)
• Super King (198 × 200 cm)

Always match the topper to the mattress size, not the bed frame size. Some UK bed frames are wider than the mattress they hold (especially divans with built-in valance).

Quick recommendations

• Side sleeper with mild back pain: 4-inch microfibre. SAIMAZ 4-inch hypoallergenic topper.
• Back sleeper, firm mattress: 3–4-inch medium-density microfibre.
• Hot sleeper: Microfibre over memory foam, every time. The breathability difference is huge.
• Just want spill protection + a tiny bit of cushioning: A quilted mattress protector, not a topper.

Browse the full mattress protectors and toppers collection – free UK delivery on every order.