Yeah, yeah, 5BX is great! While a certain rare exercise machine gives the most relief, one simple 5BX back exercise (chart 1, exercise 3) is as effective, provided I do it regularly.
I do other exercises too: stationary cycling, rowing and treadmill with some weight work. All necessary because I enjoy food!
Six years ago I started on the RCAF's old 5BX program (a quick Google search will lead you to the booklet that describes it -- dead simple) and, in exchange for 11 minutes of exercise a day on an open floor, had the body I've always wanted within a year.
I've since moved on to weights and other gym-like stuff and have not had back pain in years.
It's so stupidly obvious I'm kicking myself for it now: If you have decent muscle to support all those bones and tendons up your back, they won't be straining themselves to the point of pain while supporting your body.