Here are the things I’ve bought in the past five years that have made my office more comfortable for me.

A good chair. Not a gaming chair but a chair that’s meant to be used all day every day. I got a refurbished steel case leap 2 for $500 a few years ago and it was worth the price.

Two large monitors. I have two of these on my desk https://www.amazon.com/dp/B072M34RQC?ref=ppx_pop_mob_ap_share

Upgraded webcam . https://www.amazon.com/dp/B088D3VXC6?ref=ppx_pop_mob_ap_share and speakers https://www.amazon.com/dp/B07DDK3W5D?ref=ppx_pop_mob_ap_share

A large enough desk to spread out on. I bought three Ikea alex drawer sets for $90 each https://www.ikea.com/us/en/p/alex-drawer-unit-white-00473546/ and a 98" countertop for $90 https://www.ikea.com/us/en/p/saeljan-countertop-oak-effect-laminate-30439216/.  I have an 8 foot desk with plenty of space for spreading out and 2 monitors for $360.    https://imgur.com/gallery/UmQP2oS

A small space heater for my feet since I’m in an unheated attic.

A tiny humidifier for the winter https://a.co/d/5ivJn8F