For very short intervals (I sit...). For a long time I tried observe social norms by sitting like able bodied people, ignoring the increasing pain I was feeling. Now I try fit into my own norm instead, corny as it may sound. And I can manage my pain better (after three back ops). If I'm eating out, I'll probably get up to walk or stretch about four times. I bring a support cushion and pick the best chair where I can easily get up from. I bought an electric standing desk from IKEA for home too. In a car, I take front seat which can recline back at intervals. Flying, I take an aisle seat and move around a lot. Outside this I try practice engaging my core when sitting and breathing exercises. Best of luck finding what works for you!
I have hypermobile joints and I can only be comfortable basically sitting like a pretzel. Sitting normally in a chair with my feet flat on the floor drives me nuts and just feels wrong. So, usually my legs are crossed or I'm sitting on one of them, or have my feet up, etc. I know it's bad but I can't help it.
I reposition myself frequently, and try to get up and walk around a little occasionally
I also have joint hypermobility as well as fibromyalgia and the best thing has been buying an electric recliner chair, it means that unless I'm in such a major flare that I need to be in bed, I can get comfortable in the chair without seizing up after a short time.
I have to rotate my positions between sitting, standing, walking, resting, and lying down. The more I'm on my feet the worse I hurt at bedtime. I'm about to have my 4th neck surgery. And I change out my bed pillows at least every 8-10 months due to my neck issues. We have to buy new mattress about every 6-7 years, due to my spine, and chairs every 4-6 years. I pace activity with frequent rest periods and must elevate my legs throughout the day due to circulation issues, fibromyalgia and sjogrens that cause muscular pain, neuropathies, and vascular burning and stinging. I also wear compression hose...ugh, sweaty & uncomfortable but a necessity! Hugs love & prayers you can find methods to help you cope better throughout your days. 🙂💕🙏🌼