I'm a huge fan of inescapable bondage and the feeling of tight mummification......love bondage bags and extended sensory dep. I stumbled on this Czech maker of bondage sleeping bags (a Google search shows "sleeping bag" bondage is actually a big thing.)

Not much on the website but his Facebook site linked on the webpage has a ton of photos. Internal sleeves for your arms and legs as well as attached vest zipped around your torso combined with locking zippers and I expect this would be pretty much escape proof! Several models offer double layers with 6+ lbs of hollow fill insulation and complete head to toe coverage other than some small breathing grommets. I would think this would be incredibly severe from a heat and claustrophobia POV.

The idea of a Mistress zipping you into this, snugging the straps tight and then saying "I'll be back in X hours" is incredibly hot (pun intended grin )

https://zips-down.com/

Detailed photos here

https://www.facebook.com/photo/?fbid=6014351571926178&set=pcb.6014351898592812