I've got a Boss Design Delphi DEL/2: https://www.bossdesign.com/product/delphi - acquired 20 years ago when my then employer shut down and didn't need a boardroom any more. It's not obviously designed for computer work, as it's not terribly adjustable (seat rotates and tilts, height is adjustable, that's it), but I find it supremely comfortable.

(It also feels very solid: the mechanisms are still quiet, despite lack of maintenance, and there's very little play when I'm sat in it.)