if you google a chair for a guitarist it tends to throw up loads of drum stools.

So no back support whatsoever.

Similar with better posture the recommendation being you perch on your sit bones with a reasonably straight back stacked up on these sit bones.

Chairs with a smaller back support are maybe designed for working at desks rather than playing as we would sit forward a little but at least then you would have some support as you take a rest period.

As it's very much a personal choice I guess it will be lots of trial and error.