I've had very good success with the use of curtains. Not too heavy. Not too thin. Going with enough fabric to be 1.5 to 3 times the rod length produces enough folds to act as difusion. About two to three inches off the wall are where mine will wind up... again. They'll also hide the ginormous screen that's new too.
The heavy ones in the pics of my rig are now at the rear of the room instead.
I'm adding also some corner Chunks to each side, and some immortal (silk) plants about the speakers too. I'd hope they work out for first reflection points too, so I don't have to make panels as well.
BTW Curtains on that wall will hide other panels, egg crate foam, etc. yet still allow them to be effective.