A listening space should be treated like a recording studio. Microphones are nothing more than a set of good ears. They require the same acoustic conditions to process a pleasing sound. While there are admittedly some studios and mixing rooms that are over the top in their treatment (Blackbird Studio C - look it up - it has the famous George Massenberg treatment. Awesome.). There are many other world class studios that are nothing more than a set of heavy drapes on the wall and a few area rugs.
Room treatment is really not that complicated. It does take a little experimentation but that’s part of the fun. All you’re trying to do is knock down or diffuse a sound wave on every hard, reflective surface. The diffusion device doesn’t need to cover every inch of hard surface, not even close. But every reflective surface should have something that absorbs and forces sound waves to either change their direction or their speed. Different frequencies travel at different rates. When you knock down a certain band, they no longer travel as a standing wave and, in most cases, will cancel each other out. In layman’s terms, knocking down just one frequency band usually tames the rest. Don’t try to over analyze it.
When I treat a room, I spend a lot of time clapping my hands together or yelling a single sound and listening. If you hear the sound reverberate, your room needs more.
For the OP’s room, I’d start with an area rug - as big and as thick as the space can handle. I’d also replace all the framed wall hangings with 2” thick decorative acoustic art prints. The alcove in the background is problematic. That’s an echo chamber. Some acoustic treatments on those walls will go a long way in producing a focused bass. If you want to display a diploma or certificate, you can send a high rez photo to Acoustimac and they’ll make your certificate in to an art print. https://www.acoustimac.com/acousticart
The corner shelving unit is also an issue. Try to find some of those small decorative pillows with cute phrases and place them on a few of the shelves. If you want to get serious, line the back of the shelves with Guilford of Maine Sona fabric. The stuff works miracles and it looks pretty good too! It’s not very expensive.
The large blank wall above the computer monitor is definitely screaming to be treated.. A hanging tapestry, Navajo rug, another acoustic art print, etc., will work wonders. If you hang a tapestry or rug, don’t mount it flush to the wall Hang it from a curtain rod or similar.
Scatter a few large pillows around on the furniture.
Finally, I’d call a window treatment company and inquire about some nice fabric curtains or, at least, some heavy fabric blinds for that window.
After that, there are corner bass traps, ceiling treatments, etc., but I think you’ll already be enjoying a night and day difference and won’t care about doing more.