I had the Klymit pad a few years back… and like you, I found it terrible. It was worse when blown up fully. Killer on the ribs, especially while lying on my side. I under-filled it some, and it was still quite uncomfortable. I had problems with my hips bottoming out too, not just when moving around, but even when lying still, no matter if the pad was filled fully or not. (And for the record, I was about 200 lbs then, so a little heavy, but I didn’t bottom out on any of my other air pads.) I ended up selling the pad.
If you wanted to keep it, like others suggested, layering a CCF pad on top would help some, but IME, the popular 1/8″ CCF pad did not help… just wasn’t thick enough. The 1/4″ pad would be a bit better… but still, you have to ask yourself if it’s worth keeping with all the trouble…
If you were happy with the ridgerest, I would suggest just getting another one. As you found, the CCF pads do wear out over time, so even they are not perfect and need replacing with some time.
Also, FWIW, I too have some back issues (actually currently recovering from my second microdiscetomy) and I find flatter pads to be of more comfort than those with ridges. The NeoAir’s are mostly flat, and is my choice pad for all but summer hiking (too hot to use them then). When I am not using the NeoAir, I am using a ProLite pad. I love that pad! It’s self inflating (for the most part), flat, and only 1″ thick. It would likely be the very next step up from a CCF pad, and you may find them to be more comfortable. I would suggest trying one out.