Art, and don't be afraid to hang it high (and low). I saw a picture of a wall like this that had art hung with the straight edge on the bottom, and thought it was unique, attractive, and interesting.

Like this.

I think a nice wallpaper would make an amazing background (I think wood paterns will look gorgeous).
Also, for the lighting I suggest either a tall lamp on the right side of the couch (in the empty space) or, since the ceiling is high, a pendant light. something like that-

Goodluck!

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