M.G.
Would he fit into diapers at this point? My kids would not have so don't know if that's an option for you. If so, I would.
A friend of mine used duct tape to keep her son from ripping his off. Extreme measures but worked.
If you type in sleepwalking into the search bar, and this issue, you'll get answers/suggestions. This has been asked before :) Good luck.