Can you take a picture of the entire room so we can see furniture layout and the full walls. Post it here in the comments

I think shutters would look really nice.

Is that all the windows in that room? It appears to be a split basement, I can't tell if the chair rail is decorative or actually a transition from the foundation the wall board. I think best practice would have you hang floor to ceiling panels in the entire corner covering all the windows. Back in the say we had a ledge around a family room with this height windows and I hung 'cafe' style curtains but that was 30 years ago when they were in fashion. Perhaps roman shades would suffice? I never find shades a finished/polished look.