Dear Max,
sounds like your hamstrings are not the complaining part of the body, although having flexible hamstrings does help one with bending. But the weakest link in the chain is most likely to be the lower back itself. Treating that has sereval options, and for myself being a MDT or McKenzie therapist, I favor this method. You write that history of LBP (low back pain) is quit long and is provocated by bending and aggrevated by sitting. Does walking (longer distancdes >30 minutes) and being on the move reduce or completely resolve your LBP? Is your back pain at is worst at the beginning of the day and increases during the end of the working day? Is getting up after sitting bothering you? (makes you feel like a 60 year old?). Are you able to stand up straight or do you need bent forward a little? Do you sometimes feel that you are out of the middle with your upper body? (deviated to left or right?)
If the answer is yes on 2 or more of the above questions you are most likely to have a derangement according to the MDT/McKenzie classification system. It would be a good idea to see a MDT trained PT. But again, that is my state of mind.....so many PT think they have found the ultimate solution to LBP.....But anyway, you should feel improvement within 24-48 hours after your initial intake and doing the appropriate exercises.
Good luck,
Sietze