Seconding this! I’m also a very fidgety sitter, but it’s actually because most desks and tables are just a tiny bit too high for me (and I’m the exact average height for my demographics, go figure). I only realized this after I sat at a lower-than-average desk for the first time, and after a full work day, I thought “huh, that’s weird, I’m much less sore than usual.”

After consulting a few desk height calculators online, I’m currently shopping around for a table or desk that will go low enough, and it’s surprisingly difficult. This probably won’t help OP on their BIFL quest, but the best option I’ve found (that I can afford) is from Ikea.

OP, try looking up some desk height calculators, and use that to guide your search. If your desk is not a good height for you, then you’ll keep putting undue strain on any chair you buy, in a subconscious attempt to get comfortable.