This was also my initial reaction: don't buy an expensive chair; buy a squat rack, barbell, and plates. ROI is extremely high. Squats and deadlifts will do much more for your posture and long term back health than sitting in a different chair and still never using your back.

My wife used to wear a wrist brace for years until she started benching. Now she never gets pain. Lifting is also one of the safest sports there is. Highly recommend it for health, especially among the nerdy crowd who may not be inclined to try it; building muscle doesn't reduce nerd cred.