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

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