FWIW, if you've got a standing (or sit-to-stand) desk, get a balance board, which'll force you into more active standing.

My only issue was my feet getting sore, fixed with a balance board with built-in standing mat. I typically work barefoot or sock foot; if you wear shoes at your desk you probably don't need the built-in standing mat, but maybe?

I've no problem sitting down at home, where I have a sit-to-stand table where I can get the ergonomics exactly right for both sitting and standing. At work, it's a sit-to-stand add-on on top of the original desk. Sitting takes a bunch of readjustment so I usually don't bother. It also doesn't go high enough that I can use a balance board. I do have a workaround: I drink a lot of water at work; every time I need to hit the bathroom, I walk down the 3 flights of stairs to ground level, then back up, then to the bathroom. I'd expect this'd work for sitting-only as well.