A cool guide on how to set up your work station

Random other info:

• a headrest is unnecessary for the purposes of sitting correctly in an office chair. Headrests tend to put your cervical spine into slight extension if you're sitting straight up.
• one thing you can't see from this angle is your shoulder abduction angle. Most office chairs are quite wide, so trying to use the armrests while you type can put an unnecessary amount of strain on your wrists. Ideal positioning for your elbows is directly below your shoulders, like where they would rest if you were standing up. Better for your shoulders and wrists.
• if you're looking for a good ergo chair, I always recommend a used/refurbished higher end chair rather than a cheaper new chair. The higher end chairs (Steelcase, Humanscale, Herman Miller, Autonomous, etc) typically have replaceable parts and sometimes will still have a manufacturer's warranty depending on where you buy it.

I'm a kinesiologist who has done a lot of office ergo work.