You could stop wriggling in your sleep.
Maybe use bands like they use to tie loads onto lorries to go around the bedframe and mattress.
Or screw wooden boards pn each side to stop the movement.
Strangely my Mattress stays put but the bedside rug shifts.
If your mattress has handles on the sides, just tie a loop, connecting the handles to the frame, long cable ties should do it.
Thanks pixie, I’ll look into that one - my current thinking is towards DIY - a couple of flat pieces of wood bolted to the side of the slats. I’ll report back!