[vhodges]

Short answer: Chair, something comfortable. Desk: any horizontal surface big enough to work on.

Longer answer:

Chairs: Gaming chairs (Noble chairs look nice), Steelcase (Leap), Humanscale, Herman Miller (Aeron), etc or just about any Ego chair from Staples/Office Depot would probably be okay.

Desk: Standing Height or adjustable (Ikea, Geekdesk). Legare (Funky toolless/knockdown) and Levenger are options as well.

For one stop shopping take a look at Branch Furniture. https://www.branchfurniture.ca/collections/work-from-home (They probably have a US site as well)

Notes: You should be getting and moving around during the day anyways. I pace a lot while thinking so I am up and down all day. But I have a good/expensive egonomic chair anyways. My desk is 64"x27" table I made for myself. My wife has the ergo chair from Branch Furnture and it's okay but not great.