Herman Miller Aeron. I use a medium, there are 3 sizes. You can tell what size by the number of dots on the top back of the seat between the netting and plastic. They're quite expensive but you can sometimes find them cheaper on eBay, office liquidations, and used on craigslist. It's notable that even for used ones the warranty is something like 10 years so if there are parts that need replacing you can make it like…
I bought one of these at a dot com bust auction around 2000 and it’s still my daily driver. +1, highly recommended.