Sitting is generally OK, but I always slouch if that's the proper term, my butt is way in front of where it should be, so I have more Formula 1 position. And I can be like that for hours without feeling any pain or major discomfort. Actually sitting straight is not comfortable after some time and I always slide down. Office worker for 17 years, prior to that school 17 years of school of +-same stuff.
Maybe some slight type of scoliosis that was never diagnosed, really don't know. Working out with free weights and climbing keeps me in check and can't complain much, not even during covid times when moving generally less. But if anybody has any clue/suggestion for improvement I would be eternally thankful.