Honey, I am a people with previous back problems. Ruptured a disc 9 years ago. Every three to four months acupuncture treatment keeps me sound in the saddle (no wisecracks, SPEEDY).
There are also wonderful stretching and yoga exercises you can do in the saddle and using one of those pilates inflatable balls.
The key is core strength (your dance will help with that). Build up that core, you will be fine.
And then, of course, you need a reliable mount (shut it, CAPS)...you don't want some young crazy thing that just wants to go all jiggy on you (OK, Speed, you can actually tee off on that, I have it coming). Stick with a gaited horse, very comfortable, smooth ride.
