Yeah, you definitely have a distinctly different reason for your sleeping problems than what most of us here have likely experienced. So odds are what has worked for us, may not be what would work for you. I'm assuming you've tried muscle relaxants, given that your problem is ultimately your back? That was the first thing I thought of when you describe what is happening. Wondering if the muscle relaxant would put you into a deeper sleep and by nature of the relaxing of the muscles, cause you to move less while asleep. Just sort of thinking out loud.

When I injured my knee, sleeping was hard because I had this fear of what would happen when I slept and moved while asleep. I found that sleeping on my couch, where I was less able to toss and turn, actually helped me. Though I suppose sleeping on a couch had its own sleep problems too. I never actually had the problem that when my body was trying to toss and turn, it woke me up because my body couldn't do it. So not really much of a comparison. But that's the closest I've got.