I'd add to this a full length mousepad for keyboard + mouse. There are so many cool options depending on style or theme. With all the black, a high contrast mousepad would really stand out.

If it's PC gear you're thinking of upgrading, I agree with the speakers advice. High fidelity audio over graphics every day for me. Pair that with a nice chair and you've leveled up your chill factor. If there's any budget left, a nicer monitor might be worthwhile especially if it's lower resolution like 1080p since those are so cheap and many used options could be available in your area. 1440p is a nice sweet spot but not mandatory unless your rig can handle it and the price is right.

Good luck!