To sleep on my back. Being a life-long side sleeper has caused a lot of shoulder and upper back problems that sometimes make it hard for me to reach out and type. I wish I'd done this ages ago. It's one of the hardest things I've had to learn.
I sleep less deep when on my back. Believe there's studies on amyloid plaque clearance differing b/n different positions. And I believe back sleeping has less of such than side.
Unfortunately for me I'm a coffin sleeper.