Foroomaco Waffle Acoustic Diffuser Panels, 4-Piece Kit, 24 x 24 in, Black | QRD-inspired sound diffuser panels use four 12 x 12 x 2 in EVA modules to scatter reflections in studios and home theaters

A rug will help. Maybe more soft surfaces. Ottoman? Bookshelf (with books at different heights/depth -- kind of like a diffuser)? Can you actually do the walls? You could look at some acoustic panels (I have panels and traps from GIK -- which are great but are a little expensive and have a ~2 month lead time). Even a few smaller 2ft x 2ft panels can make a huge difference -- had like 8 of these along the windows in my condo (floor-to-ceiling glass along 2 walls) and it significantly reduced the reflections / harshness even though they partially covered only the bottom 2ft of the glass. You can also get diffusers if the acoustic panels aren't your thing / look (GIK also makes those; you can find waffle-style ones on Amazon too).