A firm mattress is not always a bad mattress. Often the springs and foam underneath are fine and the top inch or two just feels harder than you want. A topper fixes that for a fraction of what a new mattress costs. The catch is picking the right loft. Too thin and you will not notice it. Too thick and the bed feels unstable. This guide covers how thickness and GSM work, which loft fits which mattress, and where a 550 GSM topper or a 1000 GSM topper makes sense.
Not sure which pillow size to buy? Our standard vs queen pillow size guide shows which pillows fit a 60-inch queen bed.
How do you know if your mattress is too firm?
Lie on your usual side for a few minutes and notice where the pressure sits. A mattress that is too firm pushes back at the shoulder and hip instead of letting them settle in. You may feel your body resting on top of the bed rather than in it, or find yourself shifting positions more often to get comfortable.
Firmness is also relative to how you sleep. Side sleepers usually want more give than back sleepers, because the shoulder and hip carry most of the weight. A mattress that suits a back sleeper can feel like a board to someone who sleeps on their side.
Before you buy anything, rule out a mattress that is actually worn out. If you can see a sag or a permanent dip, a topper will cover it up for a while but will not stop it from growing. A topper works best on a bed that is structurally sound and simply too hard on top.
Does GSM tell you how thick a topper is?
Mostly, yes. GSM means grams per square meter, and it measures how much fill is packed into the topper. More fill gives more loft, which is the height and softness of the top layer. A 1000 GSM topper holds roughly twice the fill of a 550 GSM one of the same size. We explain the full comparison in our 550 vs 1000 GSM mattress topper guide. We do not list an inch measurement for either topper, because loft changes as the fill settles and gets shaken out, so GSM is the more honest way to compare them.
Fill type matters too. A down alternative fill is made of polyester fibers that mimic feather down. It compresses under your weight and springs back, so the topper keeps cushioning you night after night instead of going flat after a few weeks.
Which topper loft matches which mattress?
| Your mattress | What you feel | Topper to try |
|---|---|---|
| Slightly firm, still supportive | A little hard at the shoulder and hip | 550 GSM, medium plush |
| Firm all over, you sleep on your side | Pressure points, not enough give | 1000 GSM, ultra plush |
| Very firm or an old, flat bed | Hard surface, no cushion left | 1000 GSM, ultra plush |
| Firm and you sleep hot | Hard surface, warm at night | 550 GSM, less fill around the body |
| Soft or sagging in the middle | A dip that keeps growing | Neither: replace the mattress |
When is a 550 GSM topper enough?
Choose 550 GSM when your mattress is close to right and just needs the edge taken off. It adds a medium plush layer, so you still feel supported and your hips do not sink lower than the rest of your body. That makes it a good fit for back and stomach sleepers, and for anyone who runs warm, since less fill means less trapped heat.
It also suits couples who disagree. If one person wants a softer bed and the other likes it firm, a medium loft is the compromise that rarely feels wrong to either of them.
When do you need a 1000 GSM topper?
Go to 1000 GSM when the mattress is properly hard or has lost its cushion. The extra fill gives a deep, hotel-style pillow top that lets the shoulder and hip sink in. Side sleepers tend to notice the difference most.
Our best 1000 GSM mattress topper guide covers who benefits most from that much fill.
The trade-off is heat and stability. More fill insulates more, so if you sleep warm, 1000 GSM will feel warmer than 550 GSM, even with a breathable cover. The bamboo viscose surface helps move moisture away from the skin, but it cannot cancel out the extra insulation. And a very thick topper sits higher on the bed, so check that your sheets and the topper's skirt fit.
Will a topper fit your mattress and sheets?
Both of our toppers are queen size, 60×80 inches, with an elastic deep pocket skirt. The 550 GSM topper fits mattresses 8 to 20 inches deep and the 1000 GSM topper fits up to 21 inches. If you already use a quilted mattress pad, the topper goes over the pad and the pocket skirt holds it in place. Then measure the mattress, pad and topper together before you buy fitted sheets, since the stack adds height.
If you are not sure whether you need a topper or a pad at all, read our guide to mattress pad vs mattress topper. A pad protects the mattress and adds a thin layer of padding. A topper changes how the bed feels.
Does your sleep position change the answer?
Yes, more than most people expect. On your side, the shoulder and hip press into the mattress, so a firm bed leaves them with nowhere to go. A thicker topper gives those two points room to sink while the waist stays supported. That is why side sleepers usually do best with the deeper 1000 GSM layer.
On your back, weight spreads across a larger area and the hips should stay roughly level with the shoulders. Too much sink-in works against that, so a medium 550 GSM layer is the safer pick. Stomach sleepers are the same: a thick topper lets the hips drop, which is the opposite of what you want.
If you change positions through the night, or you share the bed with someone who sleeps differently, start with 550 GSM. You can always layer more cushion later, but you cannot take loft away once you have gone too thick.
What mistakes make a topper feel wrong?
- Going thicker than the bed needs. A slightly firm mattress under 1000 GSM can feel unstable and warm.
- Judging it on night one. A new topper arrives compressed and needs time to expand.
- Skipping the sheet check. The mattress plus topper stack is taller than the mattress alone, so fitted sheets that fit before may now pop off the corners.
- Using it to hide a sagging mattress. The dip keeps growing underneath, and the topper just follows it.
- Never shaking it out. Compressed fill clumps, and the loft you paid for slowly disappears.
Why choose a bamboo viscose cover?
The cover is where the topper meets your skin, so it matters more than it looks. Bamboo viscose feels smooth and silky and breathes better than a plain polyester cover. Pair that with a down alternative fill and you get a plush topper that does not trap as much heat. For more on the fill itself, see our down alternative mattress topper guide.
How do you care for a thick topper?
Both toppers are machine washable on a gentle cycle in cold water, 30°C or below, with no bleach. Tumble dry with no heat, then shake the topper vigorously for up to five minutes to bring the loft back. Give it 24 to 48 hours to regain full fluffiness before you put it back on the bed.
Shake it out every few weeks between washes too. A topper that gets compressed by body weight every night loses a little loft over time, and a quick shake keeps the fill from clumping.
Should you replace the mattress instead?
Sometimes. If the bed is more than eight to ten years old, has visible sagging, or feels uneven even with a topper on, the support layers are likely done. A topper is a comfort fix, not a structural one. Where the mattress is still sound and you simply want it softer, a topper costs far less than a new mattress and takes a minute to put on.
How long should you wait before judging a new topper?
Give it at least a few nights. A new topper arrives compressed from packing and needs time to expand, so it will feel flatter on night one than it will by day three. Let it breathe on the bed for 24 to 48 hours before you decide how it feels.
Buying a topper and a pad together? Our Black Friday and Cyber Monday offer takes 10% off when you buy two qualifying items.
