Before you decide on the wall, consider, first, a rug.

Can the sofas face each other and the electric (?) keyboard go under the window? Putting a large sofa there goes miles to filling that wall. It will also allow you to get a good sized coffee table.

Contemporary Trellis Design Area Rug, Yellow, 94" X 120" · More Info

Concentrate first on decorating where "the people are". If your living space is decorated nicely with rugs, lamps, curtain panels, eye level art, accessories, etc, your wall will look light and airy, not bare.

Before you select something for the wall, work on the furnishing arrangement because it's not working. Place the sofa on the tall wall and the other sofa in front of the window. The piano needs a new home. Do you think there might be a new appropriate location? Maybe on the wall in the foyer area?

Also that small track light on the ceiling is not illuminating the center of the wall. Shining light at the very tippy top, doesn't really accomplish anything now does it.

Here are track lights on extensions. They come in a variety of lengths.

Here are some options of what you could do. Images can be blown up to all different sizes and applied to the wall as vinyl, framed prints or on canvas depending on your budget.

Paint and tape can create an interesting texture for the wall.

a large tapestry?