27% of us sleep on our backs
Viewed from the side while you sleep, your neck vertebrae should have a gentle ‘lordosis’ or inward curvature, and the rest of your spine should have a gentle ‘S’ curve. You're going to need a lower profile (loft) pillow than say, a side-sleeper. There's a space (a hollow curve) that needs to be filled between your neck/shoulders and your mattress, without lifting your head up too high or tilting your head forward.
Here's Question 2, and you're halfway to your unique Pillow Number.
