I jury rigged an ikea desk into a permanent standing desk and use an ikea bar stool without any cushioning and it actually fixed my back pain even though I rarely stand.

I think it’s because the chair forces me to sit more upright and not lean back into the backrest, since I can’t push myself closer to the desk when I sit since the chair has no wheels. And my legs are pointing down more than in a normal chair so it opens my hips up and thus there is less pressure on my lower spine.

I actually always recommend a bar height office chair and keeping the desk at standing height to encourage standing more and because moving the desk up and down is annoying. also easier to keep everything ergonomic if you don’t move it around.