I can’t help you with the chair other than to advise going out and sitting in a few until you find one you like, but I can suggest getting a silicon wrist rest [1]. I spend most of my time typing (only 8 to 10 hours) and I find they really help me avoid neck and shoulder pain.
[1] http://www.amazon.co.uk/Fellowes-Crystals-Keyboard-Wrist-Sup...