The problem with acoustic panels is having the WAF acceptability criteria fulfilled, at the same time as having the audio criteria at an acceptable level.
My listening space is certainly not as attractive as yours, as I have my home working space, my UK TV, Hifi, sim racing rig and the Sofas squeezed into it.
I have a wall just behind my head, but as long as the volume levels are kept reasonable, the system sounds fine. I don't have any sidewalls next to my speakers, so my first reflection point is likely to be the wall. I really should try and do something....

As my "cave" is on a mezzanine floor, speaker isolation was a priority, but also the volume needs to stay reasonable. The IsoPucks made a big difference. I let a friend borrow them, and he has since ordered them, as he could not believe what a difference they made.

I don't have WAF to take into consideration, as she never spends an extended period time in my man cave. But sticking rockwool on the wall behind me does not appeal to me.
It needs to be something aesthetically pleasing. I started to look at GIK panels, but getting the right images is always a challenge.