I'll second what others said about chairs and nice keyboards. If you're going to spend a lot of time using it, it might as well be a good one. Some other things that helped me with a mainly work from home life:

- A very large desk with a ton of space to tinker with things. I got an corner desk, with one wing holding an electronics workbench, and the other kept clean for working on my 3d printer or camera or taxes, etc. PC is in the center

- Monitor arms, they are just night and day better than stands

- More monitors, I went up to 3, but I've been thinking of adding more or swapping one with a lg dual up

- Stream Deck, really nice to add macros to your workflow. It's also got nice integrations with Teams and Discord for helping with calls

- Wireless headset, I use a steel series one. Very nice to be able to get up and get water or a snack during a meeting and not miss anything

- EInk notebook, I hate typing notes, and this replaced my pile of scratch pads

- Nvidia Broadcast, noise cancellation you can apply to both yourself and the shit audio your boss's laptop mic makes

Not a purchase, but I've taken the time to make some simple scripts to improve my workflow lately and it's been great. I have one that I use multiple times a day that just turns on my webcam and light, then opens OBS in virtual cam mode. When I close OBS it turns off the cam and light. It may just change 4 clicks to 1 click but it's quite nice in practice.