+1 on the Aeron. I recently started working from home a couple of days a week and bought a fully featured used one for ~400USD. Has some minor scuffs on the legs, but otherwise practically brand new. Note that there are models with no seat tilt, non-adjustable arms, etc. that you can get for ~100USD less on the used market. They also come in three sizes (A, B, C from small to large) marked by raised dots under the top back piece--1 dot for A up to three dots for C. Like Ruairioflaherty I can sit for long periods of time with no discomfort and I have some back trouble. Great chair and built like a tank. I think the arms can be removed, but it may be a bit of a fiddle to do it, or you can get one of the models without arms. You can also get different casters for hard or carpeted surfaces. As with anything ergonomic--try before you buy.