I second the Steelcase Think recommendation. I was having severe nerve problems using a basic chair (after a recent move) and tried a few iterations before I was able to get the Think. My problems instantly went away. Moreover, I can easily sit for 12 hours a day, with normal breaks, and I have no problems anymore.

It's a simple and clean design and it doesn't tear up your clothes like the net fabric Aeron. I find that the handful of adjustments that it provides are enough.