60% of all people sleep on their sides
If we looked at your back while you were sleeping on your side, we would want to make sure that you're in neutral spinal alignment i.e. we could draw a straight line through your head, neck and spine, without any deviation of these body parts to either side. We know you're going to need a higher profile (loft) pillow than say, a back-sleeper. There's a big curved space that needs to be filled between your neck and shoulders, and your mattress.
Onto Question 2, then you're halfway to your unique Pillow Number.
