I wanted to get a
swopper for a long time, but wasn't willing to pay the 500+$/€ asking price. Saw
this one (pic below) in ikea lately at ~ 50$, and thought I'd give it a go -- have only being using it a few days, but am getting used to it, and I like it so far.
Oups -- just now, I see it's described as 'standing support'

I have it adjusted so I sit with my hips slightly above the level of my knees:
The dome seat does feel very 'pushy' -- a bit too firm. Takes a bit of getting used to. Also if you sit incorrectly (which is easy to do), you can go numb down there, even my legs went numb initially. But I seemed to quickly / intuitively find the right way of sitting. Disclaimer: I've learned to sit upright without support via the
Gohkale method, so this wasn't a big change for me. The design of the stool though does push you towards sitting with a straight back.

NILSERIK
My niece had another from them, a 20$ office chair called
ALRIK.
I was amazed by this one - just has support in small of the back which pushes the back straight. I sat in it for (just) a while and found it very comfortable.