Ask HN: What kind of chair do you sit in?

Getting older or spending too much time hunched over the computer desk has led to significant back pains...

Assuming most of HN readers spend a whole lot of time at their desk, what kind of chair do you use to prevent or relieve back pain? Do you have a specific regimen of work/rest to prevent issues that may arise? Has anyone tried a Swooper Stool or similar "outside the box" seating options?