There is contrast between the traditional furniture and the focal point of the floor which pops, draws attention. I would recover the sofas in cream colored soft fabric - suede. I would leave the curtains grey, and put down a large neutral area rug. The edges of the room would show the pattern of the floor. I would color the wall and add texture to it, but not too dark as the room will appear smaller. Add a picture and put a nice plant holder, large vase in the left corner of the room - an oriental-style vase. Or, a cream-stripe fabric on the sofas. You could go soft or bold in this room - depending on your taste.

I'd go for make it white; then right there, flop one nice little white overstuffed loveseat or something that fit, or one big whopping chair, and fit in a tiny table and light; treat that corner as it's very own micro-retreat, and the seating is to not face out into the room. Like little lounge spots put under stairs, make this one dedicated to the view; and make it minimal. Decorate the rest of the room as if the column and retreat bit isn't there.

Leather sofas can really dominate the room and can give an overall cold feeling. I would add some earthy elements, like a wood coffee table with glass or metal. Go to Restoration Hardware's website and look at their sofa room scenes. And I'm sorry I think the art is too harsh for the room. That's all your eye goes to in the room. too overpowering. I would look for something softer or maybe a cool mirror and I would add color to the room with pillows and some colorful lamps. I also think woven blinds would look great. They add warmth and give a finished look. The color of your window treatments should contrast your wall color a bit, not match it or else it starts to look generic and blah.. You have warm walls, warm floors and the woven blinds, like Hunter Douglas brand would pull it all together for you.

Just because you want to use the space below the stairs, do not just add drawers or shelfs unless you reaalllyyy need it. I would suggest go for adding something green to your house. Its healthy by adding air purifying plants. These plants are nowadays available in most of the nurseries and moreover Green patch in the house gives a beautiful look to the house and is also good for eyes ( the green color). Below are few picture to motivate you for Green patch or Indoor garden.