I'll go against the grain slightly here and recommend a regular office chair. A lot of the "gaming chairs", like other "gamer" branded things, are gimmicky or overly expensive because of the name brand or because it's been "gamerfied" somehow.
I'm a big guy and I recently picked up the Amazon Basics Big & Tall Executive Chair, and its been great. Comfy, huge
(even I feel a little small in it), and hefty. Any kind of middle-of-the-road office chair should be more than enough.
As for headsets, that's a whole other beast to deal with. My recommendation there would be, rather than a headset, a high quality pair of headphones, and a good, standalone mic. You and your buds get the best of both worlds: high audio quality and a mic that doesn't sound like a drive-thru speaker. Not sure what your budget is but in terms of brands:
My account is too new to post specific links, but in my experience all these brands are high quality and give good bang for your buck. The price ranges are pretty wild though so some may be well out of your budget.