The short answer. Most people need one pillow, at a height that keeps the neck in line with the spine, plus a second thin one for reading. Four pillows is a hotel styling decision. The height test takes thirty seconds and you can do it with a towel before you buy anything.
I slept on two pillows for years because two pillows is what a bed looks like in a photograph. Then I slept in a hotel with one good pillow and woke up without the low ache across the back of my neck that I had assumed was just how mornings were.
It was not how mornings were. It was how two pillows were.
The height test, before you buy anything
Lie on your side, on your bed, with your usual pillow.
Now look at the line from your tailbone, up your spine, to the base of your skull. That line should be roughly straight and roughly parallel to the mattress. Not level with the ceiling — parallel to the bed.
If your head is tilted down toward the mattress, the pillow is too low, and your neck is being bent sideways for eight hours. If your head is propped up so the chin drops toward the chest, the pillow is too high, and your neck is being bent forward for eight hours. Both feel fine for the first twenty minutes and both are why you wake up with a stiff neck.
Here is the cheap version of the same test, which is what I would do before spending anything. Lie on your side. Get someone to look, or use your phone camera on a timer. Then take pillows away or add folded towels until that line is straight. Whatever stack height got you there is the height you are shopping for.
For most adults on most mattresses, that is 10 to 14 cm of compressed height for a side sleeper, and 6 to 10 cm for a back sleeper. Stomach sleepers need very little — often a flat pillow or none — because the head is already turned.
What each sleeping position actually needs
Side sleepers need the most height, because the shoulder creates a gap between the mattress and the head. The pillow has to fill that gap without lifting the head above the shoulder line. This is why side sleepers are the people most often sleeping on a pillow that is too flat.
Back sleepers need a pillow that supports the curve of the neck without pushing the head forward. A medium pillow, or a shaped one with a raised edge. A high pillow here is what produces the chin-to-chest position that leaves you hoarse in the morning.
Stomach sleepers need almost nothing. If you sleep on your front, a thin pillow under the head or none at all, and if you want support, put it under the hips rather than the head. A stomach sleeper on a high pillow is spending the night with their neck turned and extended.
Combination sleepers — which is most people, whether they know it or not — need a pillow that can be squashed into a different shape at three in the morning. That is an argument for down or a soft synthetic, and an argument against anything rigid.
Why two pillows is usually one too many
The second pillow is almost always doing one of three jobs, and none of them is sleeping.
Propping you up to read. Fine. Keep a second thin pillow for that, and push it off the bed when you turn the light off. This is a genuinely good use of a pillow.
Making the bed look like a bed. This is the real reason. A made bed with one pillow looks mean in a photograph; a made bed with four looks like a hotel. That is styling, and you are the one sleeping in it.
Compensating for a pillow that has gone flat. This is the most common one and the most worth noticing. If you need two pillows to get the height you used to get from one, the pillow is dead, not insufficient. Fold it in half. If it does not spring back, the fill has collapsed and no amount of stacking will fix it properly.
The two-week test before you replace anything
Before buying a pillow, spend two weeks sleeping on a stack you have assembled from what you already own. It sounds like nothing and it answers the only question that matters, which is what height you need.
Night one, remove a pillow and note how the neck feels in the morning. Night two, keep that, and try folding a towel under the pillow to raise it by two centimetres. Night three, take the towel out and put one under the fitted sheet instead.
By the end of a fortnight you will have a number, roughly, and a clear sense of whether the problem was too much height, too little, or neither. That last result is the most common one and the least satisfying: sometimes the pillow is fine and the neck is stiff because the pillow is fine and something else is not.
The reason to do this rather than reason about it is that pillow height is one of the few things about a bed you can actually test for free. Mattress firmness, sheet fibre and duvet weight all need a purchase first. Height does not.
Fill, honestly
Down compresses to your shape, breathes, and lasts. It is expensive, it needs washing carefully, and it is the wrong choice if you are allergic to feathers. It is what I sleep on.
Down alternative is polyester pretending. Cheaper, washable, and it goes lumpy in a year or two. A reasonable first pillow.
Memory foam holds its shape and does not move, which some people love and some people find claustrophobic. It does not wash. It also gets warm, which matters if your bedroom is already the warm room described in why your bedroom feels stuffy by 3am.
Latex is springy and durable and heavy. Good support, less mouldable than down.
Buckwheat is a bag of husks you shape by hand. Surprisingly good for side sleepers, noisy, and it smells like a field for the first week.
The honest summary: fill decides how the pillow behaves over the night, and height decides whether your neck is straight. Height matters more, and it is the thing you can measure before buying.
The thing nobody does: wash it
A pillow is against your face for a third of your life. It absorbs sweat, skin, and everything your hair carries. The protector goes in the wash monthly; the pillow itself wants washing two or three times a year, which most pillows will survive and most people never do.
A washable cotton protector is the single cheapest way to make a good pillow last. It costs less than a takeaway and it is the difference between replacing a pillow every eighteen months and every four years.
What I would actually buy
One medium down pillow, at the height the towel test told me. One thin spare for reading. A cotton protector for each. That is the whole purchase, and it is less than the four-pillow arrangement I had before.
If you are a committed side sleeper and down feels too soft, buy the firmest pillow you can find and take fill out of it until the neck line is straight. Almost nobody does this, and it is the reason almost nobody has a pillow at the right height.
