Im totally with Martin on this one.
I suffered a prolapsed L5 disc in Oct 2010, which took me off my feet for 2 months. I could not sit or stand for more than 30 seconds before the pain became crippling. I spent 2 months on my back, dosed on pain killers/anti inflammatory drugs till I had my 2nd cortisone steroid injection. I had to eat like a dog, and could not go to the bathroom/shower without assistance. Anyway - forget the past...
A couple of points..
a) after the injection and more rest, I took it very easy and slowly over the course of a year have built up from gentle physio/swimming, to regular pilates and weights at the gym. It is a huge help! I feel the difference if I miss a pilates session (you need a good instructor though, bad instructors can do further damage)
I have found the Z seats and driving position one of the most comfortable I've had. The only point at which I have to be careful is when exiting in the car - I breath out and engage my core muscles before exiting... as it can be awkward in tight spaces.
The issues that upset my back are tight hamstrings and weak core muscles (as I have a desk job). Only cure for me is to keep moving, exercise my core and stretch the hamstrings as much as possible.
Is your injury treatable? Or have you been told it is with you for life?
If there is a way you can sort your back out, getting your back better will bring more benefits than changing your surroundings to suit your injury.
Hope you get better soon - I know how horrible back pain can be.