If you're looking for a really comfy great quality built "big boy" chair that does not require you to take out a second mortgage ... I recommend the
Sealy Posturepedic "Geneva" Highback Executive Chair ...
I've had mine for 2 years or more now, and its my favorite of maybe more than 8 under $400 office chairs.
I'm 280 pounds, and was 330(ish) when i bought it!
It has the tilt mechanism, pneumatic gas lift, and
turn-dial lumbar support 
(best feature of the chair IMHO)
I think I got mine at Staples for $299.99