A pillow has one job: keep your head in line with your spine so your neck muscles can switch off for the night. Everything else — cooling, materials, price — is secondary to getting the height right. The height of a pillow under load is called loft, and it is the number almost nobody shops by, which is why so many people cycle through pillows without solving the problem.
STEP 1: FIND YOUR LOFT TARGET FROM YOUR SLEEP POSITION. Side sleepers need the most loft, roughly 5 to 7 inches, because the pillow has to fill the entire gap between the ear and the outside edge of the shoulder. Back sleepers need medium loft, roughly 3 to 5 inches, enough to support the natural curve of the neck without pushing the chin toward the chest. Stomach sleepers need the least, 2 to 3 inches or a flat pillow, because anything taller cranks the neck backward for hours. Combination sleepers should size for their dominant position and choose a fill that can be reshaped.
STEP 2: ADJUST FOR SHOULDER WIDTH AND MATTRESS FIRMNESS. Broad-shouldered side sleepers need to add roughly an inch of loft; narrow-shouldered sleepers subtract one. Mattress firmness moves the target the other way: a soft mattress lets your shoulder sink in, which closes part of the gap, so you need a slightly lower pillow. A firm mattress keeps the shoulder proud and requires more loft. This is why the pillow that worked on your old mattress can feel wrong on a new one.
STEP 3: CHOOSE A FILL THAT HOLDS THAT LOFT. Solid memory foam and contoured foam hold their height all night and are the most predictable choice, but they respond slowly and can trap heat. Shredded memory foam is adjustable — you unzip it and remove fill until the loft is right — which makes it the safest pick if you are unsure of your target. Latex is springy, breathable and very durable, with a firmer feel than foam. Down and down-alternative are soft and moldable but compress under your head, so the loft you feel at midnight is lower than the loft on the shelf; they suit stomach and back sleepers better than side sleepers. Buckwheat is firm, highly adjustable and breathable, but noisy and heavy.
STEP 4: MATCH THE FILL TO YOUR PROBLEM. Sleeping hot points to latex, buckwheat, or a foam pillow with a phase-change or perforated design rather than a solid memory foam slab. Neck pain usually points to a contoured or adjustable pillow so you can dial the loft precisely. Allergies point to a washable fill plus a zipped encasement rather than down. Snoring or reflux points to a wedge or an adjustable base rather than stacking pillows, which bends the neck rather than raising the torso.
STEP 5: TEST IT PROPERLY. Lie in your normal position against a wall or have someone photograph you from the side. Your nose should line up over the center of your chest and your chin should be neither tucked toward your throat nor tipped back. If you find yourself folding the pillow in half, the loft is too low. If you wake with a stiff neck or you have to slide a hand under the pillow, it is too high. Give any new pillow a week — the neck adapts.
WHAT NOT TO SHOP BY. Thread count on the cover tells you nothing about support. Fill weight in ounces is not comparable across materials. A firmness label on a pillow is not standardized between brands, so a 'medium' from one company can be an inch taller than a 'medium' from another. Loft in inches, adjustability, and return policy are the three specs worth comparing.