I use the foam wedge panels from Studio Spares https://www.studiospares.com/acousti...5mm-465300.htm on the door (which was giving off a distracting flutter echo) and on first reflection point. Cheap and get the job done but I am not really bothered about looks - although I think they look okay.
Helps to start with a good room which you seem to have. Then you don't really need to do that much.
I might be moving in late spring and new room is an acoustic nightmare.