I have maddeningly intermittent back problems due to multiple sports injuries. Spring mattresses are generally OK to sleep on, it's next day that I can't sit upright, only slouch. Years ago a doctor recommended a waterbed or foam mattress. Waterbed no. I've slept on a 4" foam mattress for 25 years now. This foam slab costs only a few hundred $, and I replace it every decade or so. Foam shops sell standard mattress sizes. I put it on a sturdy futon frame. Downside (for some) is it's low to the floor, but upside is no room for monsters underneath it.
re: getting jiggy. No problems, and it never squeeks. No complaints either, it's forgiving on the knees, and, ahem, pushing a face into it. You may find 'developing a new rhythym' is appreciated.
antaeus