Do you plan on painting your walls? I hope so. If yes than could also change your plan later. Be sure to look at the entire room before deciding how to decorate just one wall. I would consider a greige tone on the walls. As you have natural wood baseboards..(I like them), I would add tall shelves, the color of your trim to each of the alcoves. The bottom of the alcoves could be closed cabinets. Your TV could sit on one of them. Leave the backs of the shelves open for the paint to show through. You could display other art (including paintings) on them as well as books, photos, etc. I would not put a mantle above the fireplace as it looks more contemporary to be a clean look. I would place a very large framed round mirror over the fireplace, or a very tall vertical one, If every mirror were to only reflect a great view..there would be very few of them anywhere.

I think the room could be much more elegant if you dry walled the end of the pony wall up to the ceiling which would give you a more centered fireplace which could then turn into a focal point with a proper mantel. Right now the set-up looks sort of busy and odd, especially with all the books in the built-in. If you chose to do that I would get rid of the bookcase. If you want to keep the current set up, beefing up the wood on the mantel as Scott Design suggested would be an inexpensive way to improve its appearance. I would also remove the books and put in a few art objects in the bookcase.

Gorgeous sofas! Would you consider using the Thibaut print suggested by Judy G Designs in a soft fold Roman shade? You don't say how many windows there are in the room. But Straight edge on the bottom, outside mount, clean and simple. The print has enough activity.

Simple is the right style for the fireplace. But that means you can't crowd it with large furniture or it easily gets lost. Can you rearrange the furniture?