I have owned multiple expensive office chairs. The three brands that I recommend the most are Steelcase, Herman Miller and HumanScale. I would suggest sitting in a few models of each brand as they all have pros and cons. There are also many versions of the same chairs, but the level of adjustment raises the price. If the price for a new one deters you, you can find many office liquidators with a Google search. Many have eBay webpages, but if you can find a warehouse close to you, I suggest going to see the chairs in person as they can vary from almost new to used to refurbished. FWIW, after using multiple chairs from these three brands, I have found the Steelcase Leap to be best for me. I used a preowned leather one for about 5 years before treating myself to a brand new one. I like this chair the best for me as I can lean back with my feet up and still get the support I want. My friend hates my chair and only likes his HumanScale Freedom. This is a very personal decision, but in the models that come with an optional headrest, I suggest always choosing that option. Also, you mentioned chairs for bigger people. I know the Aeron chair does come for an option for larger people as I actually had that one in my office at one time.