Hiya - commiserations on the back problems!!

Not a happy place to be, and I feel your pain (literally!!). I have back problems, partly genetic partly due to injuries, and have had them creeping up on me over the years. I am converting all my garden area to raised beds, using straw bales, as I can sit on the edge while I tend them with hand tools.
I work carefully, slowly, pausing to stretch often (I don't know if your condition makes this possible for you), and know my limitations well. As soon as I feel a twinge, I stop and go in and put a heating pad on it, and that usually really helps. I'm to the point now where I can work for about 3 hours at a series of different farm activities, but only spend about 15 minutes doing each one. It's kind of a pain, because I used to really like getting stuck in to one activity, and plugging away until it was done. I can't make a raking motion, so I've learned to use the rake like a broom, and that works really well, again, as long as I don't do it for more than 10-15 minutes at a time. I also warm the real trouble spots with deep heat before I go out to work, and really helps trouble from happening.
Sorry to ramble on so, but I know what it's like to work with those kinds of limitations. Hey, could be worse, not meaning to be flip, but I'm not in a wheelchair. Yet.
Cheers
Andrea
NZ