Martin, whatever exercise you do, you must check with your doctor first, you dont want to cause further damage to your spine.
Your doctor might even prescribe youy a few sessions at the gym with a personal trainer, you should ask, maybe you can be referred for physio and then be given exercises to do at home, or swimminng lessons, just ask around, esp your doctor/nurse, see what they can come up with.
Re diet, some people cannot do low carb/high protein, for example those with kidney problems, I used to just reduce the stodge if you like, eg if I fancied something like lasagna or macaroni cheese, I had a much smaller portion than I would have had normally and filled the plate with looads of low carb/GI vegetables; I am a greedy guts, for me it wouldnt work to have the plate just half full, or something, my word I would have given up the slimming.
Sometimes when I was too busy to cook, I used to get a ready meal from the supermarket and have either a huge salad with it or again a whole load of cooked veges, dessert was low fat yogurt mainly or lower GI fruit or even a couple of biscuits.
Now I just do the wholefood/mediterranean foods, completely free of chemicals, addtiives, etc and cook and bake all my food in larger quantities that I then freeze in portions, this saves me time as I have a good cooking/baking session every 2 weeks or so.
All the best
Karen