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I'm 6'3 and 250, recently got a serta chair off of Amazon, it has lots of features and is very comfortable for sitting in for hours at a time. I would definitely recommend this chair and probably other serta brand chairs for larger people. The back can be adjusted up, but I had to put a couple of bolts into the metal to keep it from falling over time. Not a huge deal, a C clamp could work as well.
Get a Serta chair with lots of adjustability. That looks the new version of what I use, it's not perfect and the lumbar... bar in mine isn't always in a good spot. But you just want something that can adjust to match a car's posture. So any chair that can adjust back angle, seat tilt, height, back height and on and on... will really help. The Herman Miller he suggested is a mighty fine desk chair, but it's a damn silly suggestion for our purposes.