in my experience the pillows matter more than the mattress itself. I have a decent futon mattress with a 3" memory foam mattress topper, and I have a billion pillows and plushies so I can arrange my limbs in whatever way is most comfortable for me at the moment. it doesn't always prevent dislocations, but it's better than nothing

Yeah I also use a lot of pillows to support myself, one between legs can help lots if you sleep on your side. I haven’t found a way to stop sleep dislocations though

I do not have eds, but my neck and shoulders love to sublux in my sleep. I have a "cervical support pillow" off of Amazon. It is thick memory foam, and its shaped really weirdly, but I will never sleep without it now. It helps my pain and bones so much.

It's all I have but definitely not a box spring mattress, I dont even understand who thought those things were a good idea to the point it's standardized but they're not. I dont actually know what's wrong with me but I wake up with a lot of dislocations. I have however almost mastered the art of pillows, even with only terrible Walmart pillows and squishmellows available. I try to make sure I have just enough support to my head that my neck is aligned with my spine the way it would be if i was sitting/standing instead of at the mercy of gravity and that has immensely helped waking up with neck pain and headaches. I got the idea from one of those cube pillow commercials as a teen and never looked back, idk if the cube pillow itself is actually good tho I never got one. I also sleep with a pillow between my knees and thighs, between my thighs helps with hip dislocations and i can usually feel my knee bones touching if there isn't a pillow there and it's a bad feeling but I'm sure it plays a hand in helping with my joint dislocations. There is one thing though, and I'll probably ask my chiro and see if I can come back to this comment with a fix, my rib keeps drifting into my shoulder blade on the side i sleep on and it feels like I got shot in the back.

Not Eds but I bought a full body pregnancy pillow off Amazon shaped like a 🧲 and the versatility of that pillow made it my favorite for any lounging I did. I felt cradled anyway I turned and it didn't impede my tossing and turning like I thought it would

So I know this is old, but I recently tried the linked pillow below. I've only been using it for a couple weeks, and I had to put about 2 inches of pillows below it for me to sleep on my side, but it's the right density for my neck. For my shoulders and hips, I use an overstuffed poly fluff body pillow. Good luck! High Density Space Cervical Memory Foam Pillow, Contour Pillows for Neck and Shoulder Pain, Ergonomic Orthopedic Sleeping Neck Contoured Support Pillow for Side Sleepers, Back and Stomach Sleepers https://a.co/d/biJ4hnZ