No two people are going to agree on the best pillow, but there are some basic rules you can follow if you want to minimize neck and upper back pain while sleeping. If you are a side sleeper, you want a pillow that is on the ticker side that offers enough support to keep your neck in a neutral position. Too soft and your neck bends down towards the pillow, but if it’s too thick your neck will bend up towards the ceiling all night. If you are a back sleeper, you want a pillow on the softer side that allows your head to sink into the pillow so that it can support the natural curve in your neck. For you stomach sleepers, a thin but supportive pillow will do the best job keeping your neck and upper back out of pain.
-- Dr Christopher Ernst, D.C.