I'm sorry to hear about your back. Mine has done the same to me several times in the last 10 years. On thing that helps when my back "goes" is a second, wide, leather belt around the waist. Like weight lifters, it allows you to use your stomach muscles to support your back. When discs break they can mend in time but they will always be a point of weakness. I'm also doing Pilates to improve my core strength.
I can hold an 8.5lb bass for 3 sets but a 9.5 bass starts to feel uncomfortable after 1 set. That's how fine things are measured these days. I've also gone for very light cabs and a trolley and I sit on a bar stool if I have to. There is some fantastic sounding gear out there at lower weights, but unfortunately they are generally at a higher cost.
I spent the money because I'm not ready to retire.