Flank the FP with the two chairs and get a larger rug that will fill the space when the sofa's front feet are on it. Glass coffee table 18" from sofa and colorful art piece above it. Build a credenza over the rad. Install plantation shutters (half way would be ok if you can't do the entire window) topped with a fabric cornice that picks up on colors from chairs and the new rug, which should be more patterned and colorful. Mount TV centered on the wall at the stairwell end of the room. Put a credenza or console under it.

Based on what I can see of your room, here is a furniture arrangement that may work well for you. It's essentially your layout with Deco's suggestion of flanking the fireplace with the chairs. I've got an ottoman in front to the fireplace and between the chairs for flex seating.

With the chairs pushed towards the fireplace you'll now have room to push your sofa forward and slide your sofa table behind it. An oval coffee table and larger area rug (as mentioned) will define your seating area.

On the wall opposite the radiator, I've placed a TV console for a flat screen TV. It's about 2/3 the width of the wall. Its generous length will give that area a little more presence. To make the wall advance into the room, consider painting it and accent color.

Definitely look into a radiator cover. There are some great options out there. Good luck!

I would put the chairs on either end of the rug so you can see the fireplace and a big coffee table in the middle. A bigger rug is needed too. I agree with deco about building a rad cover but then I would flank the windows with drapes.