You should really take time do strength exercises for your back, three or more times a week, always.
Since I started working out regularly 7 or so years ago (I'm in my mid forties), never again I had any back pains, and my sitting style is awful (I kind of melt in the chair).
I do Pilates and yoga 3-5x a week, as well as regular body weight training and surf, so am fairly fit and very focused on back and core health.
For me, it's the lack of movement during intense periods of focus - four hour blocks, over many years, sometimes 16 hr days. At least with the bad chair, I'm always moving, keeping the support muscles active. When I sit for a long time, and forget the core, I think is when compromise to key systems occur.
What I'm not good at is getting up every 20 min, if I did, I'm sure I'd be fine.
I have a tendency to forget my body when I focus, which is a plus and minus. It's great for the work, not so great for the body, so having a chair that reminds the body to be active is a plus for the long term.
Personally, I like the combo of a balance board/standing desk. As standing without the board, also caused me to collapse into a leg causing tightness, but with the balance board, I'm always in a slight state of motion, and the muscles are active, so I'm ready to go when it's time to move. As I've aged, I find my focus is actually enhanced as well.
With the office max chair, I squirmed and moved all day long, uncomfortable after 20 min. I had this chair for 6 years.
With the Aeron, I could blissfully work, and not move muscle for 4 hours or more. I had this chair for a few years.
After a few years with the Aeron, I had some awful back problems. I attribute this to my body relaxing so much in a semi upright position that the muscles were not activated enough to support the spine and good posture. Worse, when I got up, the muscles were not activated, unless I specifically did movements to wake up the correct chains.
Then I got a new job which had cheap chairs and a sit/standing desk and was here for 6 years.
Many years later, a combo therapies, balance boards, and cheap office chairs that force me to squirm, move and get up, seem to have solved the issue.
I'll never get a chair that is "too" comfortable again for work as it really messed up my back.