Thanks, I agree the current layout isn't working. I've considered turning the sofa, but the problem with this is that we like to have the window open all day as we don't get much light and this would reflect onto the TV; so we'll have to keep the blinds down all the time.

First, if you don't already have them, invest in a small package of furniture movers, those little disks (fuzzy for hard surfaces and smooth for carpeted surfaces) to place under furniture to move it easily. The are less than $20 at Home Depot. You will feel empowered to move large furniture, easily and all by yourself.
Try moving the sofa against the long expansive wall. Play with the bookcase between the sofa and kitchen pass-through. Without knowing measurements, not sure it there is enough room.
The TV could be wall-mounted on the same wall where it is sitting now, but with a full-articulating arm it can be swung out and tilted for easier viewing from new sofa location. When not viewing it can be flattened back against the wall.
Look at long panels for the large window and run them floor to ceiling. You mentioned Billy bookcases, so that means you probably have access to an Ikea. They have some very nice panel options as well as hardware types.

Spend the money to close the opening from the kitchen to the living room - you are losing valuable space and probably kitchen cabinet storage there. Then move the bookcase on that new wall and put the sofa on the wall opposite the windows. Move the black table by the bookcase to the right so it is part of the hall. You'll find you have room for a couple of chairs to flank the window two. A large rug, drum light fixture, maybe an accent color behind the TV will have things looking and functioning better.

Thanks, some good ideas here.
@decoenthusiaste - we created the kitchen opening just before we moved in to get some light in! I know it's hard to tell, but the house is very dark, particularly that corner. We will eventually convert it into a breakfast bar!

With such large windows it is hard to believe you have a dark house. Are those north facing windows?

Those windows are north facing, but because we're a ground floor apartment and have a sheltered balcony, trees, etc we actually don't get much light in. We often have lights on during the day. Very unlucky really!