Hi, this is Mary Jo and I'm your designer. I graduated from Louisiana State University with an interior design degree and have been working in the industry ever since.
This room has a ton of space! We love that you have vaulted ceilings too and that you have a good bit of natural lighting. The hard part is making the space make sense despite it's narrow length. We think that with these next suggestions you will feel like the room will have more a system and will have that depth with color/pattern that you want.
First off is the room's layout. We completely agree with you that you have a dilemma of how to make it all work with the furniture you have. The sofa and matching chair are lovely and we think they work in this space, but because of the scale and size we can't put anything else that big in without making the room feel crowded. What we would suggest is splitting the room in two with the dividing line being the doorway (on the wall where the sofa is now). The front area- being the area by the door- and the back area. The front area is where the TV is now, is where we would suggest a loveseat to put in the middle of the room, facing the TV. We picked one out that would coordinate with your sofa and chair but add some more texture into the room other than leather. We also picked out an entertainment center that would be able to fit the bookshelf's content in it as well-so that it's more seamless looking and not cluttered. The entertainment center would go in the corner, that way you will be able to open the window that it was blocking. This arrangement also gives you a chance to add a couple of accent chairs (they would be facing the TV but they would be turned so that their backs were to the closet but not against the closet doors) - this does depend on how much space you have to walk when you get in and if you can fit two or one chair. See what you think and take a couple of dining room chairs to play with so that you see how much space you are dealing with.