I have finally settled with a standing desk and an Ikea Ingolf bar stool - basic flat wood seat, no padding. As a 6'4" person, many chairs are awful, create pain, etc., but I love this setup.

The idea that having a slightly less comfortable chair would lead to more movement has proven true. It's also relaxing enough to sit in when I'm tired of standing up, but not super comfortable to slouch in, so it encourages better sitting posture.