Catventurer: My butt holder of choice is an IKEA STRANDMON Chair in Skiftebo yellow. There is enough room for my to sit comfortable and for my cat to join me. He usually sits along the right-side of me or up on the back of the chair to look down.

https://www.ikea.com/us/en/p/strandmon-wing-chair-skiftebo-yellow-20361897/

Although this chair is super cozy, I don't think it would work all that well if you're sitting at a desk.
My computer is a laptop.