The right pillow for you depends on your personal comfort preference, how you sleep, and the mattress you chose. Your pillow should support your head comfortably and keep your cervical spine in proper alignment. This means that your neck should have the same alignment that it does when you're standing up, with your head centered over your shoulders. When you replace your mattress, it’s a good time to think about replacing your pillow, too— a firm, thick pillow may have supported your head comfortably on your old mattress, but your new mattress will likely support your body differently and might make your pillow needs different as well.
How soft or firm a pillow is depends on what it’s filled with. Down and down-feather blend-filled pillows will feel the softest and most compressible and may be the most comfortable for back and stomach sleepers.
Synthetic fiber-filled pillows are soft but a little more resistant than down-fill, and may suit back and side-sleepers.
Cotton and wool-filled pillows tend to be firm and may be comfortable for side sleepers.
Memory foam and foam-filled pillows are the most firm and resistant to pressure and may suit side sleepers.
Shaped or molded pillows, made from a single block of foam, are designed to alleviate neck pain or are intended to address other conditions. If you have a specific condition that affects sleep you may want to consider these specialty pillow.
If you’re purchasing your pillow at the same time as your mattress, choose your mattress first and try out pillows on your chosen mattress in your preferred sleep position. If you’re buying a pillow elsewhere, you can get a sense of how a pillow will support your head by trying it out against a wall in the position you normally sleep. In either case, the pillow should support your head in neutral alignment with your spine (just as if you were standing up straight). Along with your new pillow, consider buying a pillow protector to protect your pillow from moisture and staining.