One Owens Corning 703 panel 2'x3'x1" will do the job, cost little, and be light as a feather. You may want to cover it with some fabric. But it will be so light and easily moveable, you could also just hide it behind the TV and only hang it in front when listening to music.
The thing about fabric, the outer layer has as big or bigger effect as the whole thing. Like nonoise got good results with a wool blanket the surface of which is rather porous. A thick moving quilt might seem better but the tight weave outer shell actually reflects more of the high frequencies we want to absorb. So keep this in mind if you do go with OC703 and select an open weave porous fabric similar to speaker grill cloth for your covering.
The thing about fabric, the outer layer has as big or bigger effect as the whole thing. Like nonoise got good results with a wool blanket the surface of which is rather porous. A thick moving quilt might seem better but the tight weave outer shell actually reflects more of the high frequencies we want to absorb. So keep this in mind if you do go with OC703 and select an open weave porous fabric similar to speaker grill cloth for your covering.