Yana
I get a little back pain caused by old age and use a shooting belt designed for the shooting trousers, they are only 40 mm wide but do help a lot, most of the clothing companies make them, Kurt Thune, Monard, etc.
I'm not a doctor but I think you are risking serious injury by trying to shoot standing whilst also trying to recover from an injury, much better to recover first. Are you tall and slim? if this is the case this will necesitate a more severe back bend to get a stable position, then its even more advisable to wait. Do you suffer in the shooting position with out holding a rifle? if this is the case then definately don't shoot.
Only you can feel the pain so it is difficult to advise, rifle set up is a matter of preference but it can help. I coach some shooters with reduced flexibility (age!) and one thing we do is to get the ballance of the rifle more towards the butt. Remove as much weight as possible from the front end, muzzle weights etc, and place it in the butt, this takes away much of the need to have such a severe back bend. Rifle ballance is more critical than the weight. Some people prefer the ballance towards the butt and find it more stable. My wife used to shoot 380+ 30 years ago, now at 60, not as flexible as she was then, has her LG300 Junior weighted up to 4.5 kilos, but no one would believe it was that weight as most of the extra weight is in the butt to get the ballance only just in front of the trigger to let her shoot 370's.
I think you may be better not shooting standing until the back is better, if you wish to continue practicing why not shoot the German Auflage style supported shooting for a few months to keep the sighting and trigger technique in practice.
Robin
Walther KK500 Alutec expert special - Barnard .223 "wilde" in a Walther KK500 Alutec stock, mmm...tasty!! - Keppeler 6 mmBR with Walther grip and wood! I may be a Walther-phile?