I recently swapped out my office chair for a coffee table. It allows me to sit without back support in a variety of positions - cross legged, feet on the ground

I recently swapped out my office chair for a coffee table. It allows me to sit without back support in a variety of positions - cross legged, feet on the ground, sometimes with my hands supporting me.. even hunched over if I'm being a bit lazy / sucked into whatever is happening on screen. The results have been almost instantaneous - back feels stronger, I'm not as stiff overall - general mobility and flexibility is better. Took a week or so to get used to. Initially I wanted to get up and go find a couch a lot. Now I can sit for hours, but like you mentioned - with the small movements - it's never totally sedentary.