I have not done this, so cannot personally attest to it, but people talk about the value of sitting on those execise balls to strengthen core muscles and balance and that this can help the back. I have been reluctant to try it because I am sure I would take a tumble, but it makes a lot of sense and I plan to try. The reason to say this is that it seems to me that one needs the back muscles to be stronger. As you say this is really hard to do when exercise is so easily overdone in this condition. It you have the patience, try tiny frequent strengthen exercises distributed through the day. It might not make a huge difference, but every little bit might help. At least that is what I keep telling myself.
I also am really careful not to carry anything heavy now knowing that my back is weaker than it used to be and therefore more susceptible to things that will make it hurt. WithHope.