Piano seat with backrest

[volcanoadam]

I've been having problems with my upper back for a long time, but recently it became quite serious problem to me. Even though I make regular brakes, both at the piano and at work, and do regular stretches and exercises, it still seems to be progressing. It's much better when I play seating on my office chair with high backrest. The problem is the backrest severely restricts my arm movements and the chair itself is a bit too low.

I did some research on suitable chairs and someone suggested using a drum throne. Have you guys any experience with those? Maybe you could suggest some other more suitable chair?
Would it be better to get a shaped seat, like that one:
 www.amazon.co.uk/dp/B000BZIYY8/?coliid=I2HRV8M4HXMVUJ&colid=1O0454VGQTNT3&psc=1&ref_=lv_ov_lig_dp_it
or would it be better to use a round one?

[quantum]

Jansen makes a few
https://jansenpianobenches.com/collections/piano-chairs

Maybe you could get an ergonomic office chair which you can remove the arms.