I picked up a Herman Miller Aeron from a guy off CL years ago. Yeah, yeah, I know Aerons have a whole fanboy mentality going for them, but honestly, it's the most comfortable chair I've ever used.
With the mesh back and seat, I never get too hot sitting in it for long periods. It's very adjustable.
And you can take the arms off, raise or lower them to whatever fits your frame.
One note, the lumbar support on the bar is a must, if the chair doesn't have one you can get them separately.
Keep an eye out and you can often bag one for 200$ or less.
If you're normal size guy, go for the C size, though (the biggest), B and A are pretty narrow.