I prefer the 'savasana' position, I actually find it more confortable without a pillow in this position, I can also be by the sides or any other position, just not for all night long, I found it actually decreased upper back and neck pains after I removed the pillow

I sleep on my side with my head on my arm.

Before going pillowless, I had a buckwheat pillow. It is less cushy and fluffy than standard Western pillows. I believe they are typical in Japan and not hard to find these days. It helped wean me off the giant fluffy Western pillows.

I have respiratory problems. I sleep better without breathing in allergens and dust mites and god knows what from a pillow. Though it did take a bit of time to get used to doing it differently from how I had my whole life.