Probably going to go with a random reasonably comfortable office chair with no arms (or removable arms).
Roc 'n Soc drum throne with optional back
Same here without the back.. has worked well for years now. I should look into the back attachment...Roc 'n Soc drum throne with optional back
I love this chair: Link to Amazon with full description
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That said, I immediately got rid of the heardrest (WAY to restrictive), and the arms (what was I thinking???). They may have a version of this without the arms for all I know. For the money, this is the best chair I've ever owned for the back, for long days in the studio, for playing guitar.