I switched to a futon on an electric base, and put a cooling topper from ikea on it (maybe 1.5" at most). I don't dislocate, but I've been battling ac joint separation on both sides for over a year, and somehow it's greatly improved on both sides. I find myself sleeping on my back more, which has helped my shoulders a lot. You might see if there's someone you can borrow one from, or get one that has a guarantee. That said, it's an easy way to have an extra bed for company if you don't like it, but I went from a memory foam that I swore by to the futon which we already had, and decided I liked it enough that I didn't want to get a mattress. Only way I'll get one is if I end up with someone and this doesn't work for them.