I love number three pic above. I think you can really go nuts with the rug and wall decor because you have a lot of neutrals in this space.

You'll want some real pattern down there since you have such large expanses of solid gray, tan, and the wall. Choose a rug that harmonizes with the tan floor, has a small amount of gray to link with the sofa, and some blue to link with the art.

Loloi Rugs Leyda Ivory / Lt. Gold Transitional Rug - LEYDLY-05IVLD7AB0 · More Info

Once you choose your rug you may want to pick up a color or two and pick pillows or throws to add some punch in this very gray room. You may also want to use one of those colors for a table covering to add some softness. Good luck.

Notice how big the sample rugs are. Don't skimp. They should slip under the front 1/3 of the seats and extend past the ends by a foot or more. Tape it out on the floor with painter's tape and measure. If it isn't a standard size, go up in size if you can.