While I can sleep on my back, I feel like I get better rest when on my side. It's not about how the pillow feels or anything like that, but my whole body and brain just seem to relax more.

Apparently [1] sleeping on the side is better for your health, as well.

[1] https://youtube.com/watch?v=O8UoAASCUsQ

Sleeping on your back is worse for the spine and worse for breathing.

I had to learn to sleep on the side after smashing a vertibrae in a climbing accident, no other position offloads the spine as effectively.

Legit question, what's the reason for wanting to sleep in what seems to be an uncomfortable position for you?

I also can't sleep on my back but have no urge to change that.

I have a lot of shoulder issues that are worsened by sleeping on my side or stomach. I also have a flat spot on the side of my face from always sleeping on it, and it gets worse the older I get. I'd like to be able to use overnight skin treatments without it getting all over my pillow.

Fair enough. For what it’s worth, I fixed shoulder problems with a combination of mattress, pillow and arm position thought the latter is less important.

I don’t have a flat face (yet?) though I can see how that could be annoying.

Wonder if making some kind of custom shaped bed (ie from memory foam) might be a useful solution?

Me too. I can sort of "trick" myself by putting a balled-up blanket on my pillow and turning my face to rest against it.

My SO used to sleep on her belly.

Then we got an overpriced mattress with the same material that NASA uses...

I'm an endless chaser of value. I hate to overpay for things. That mattress was $5k (king sized).

She sleeps on her back, and her sleep quality has measurably improved.

I like to sleep on my back, but with a pillow over my forehead and eyes (i.e., nose and mouth exposed to fresh air).

One nice thing about sleep apnea treatment (CPAP) is that you always have fresh air.