I would go light , 8 by 10, with a pattern since your floors are dark.

I agree, white with a neutral pattern. The bookcase seems out of proportion to the sofa and makes it feel a little cramped. I would consider moving it and just have art on the wall there.

Bakerhill Shag Farmhouse Moroccan 7'10" X 10'3" Area Rug · More Info

Some nice art with link.

https://www.art.com/gallery/id--a926220/sydney-edmunds-posters.htm

it depends on what style you are trying to achieve, but I would choose something lighter, but with a pattern.

Could we please see all 4 walls of the room? It seems rather cramped and I am wondering if another arrangement might work better for you.

Thanks!

Some option

Agree with the cramped feeling and you need something light to offset all the gray and the dark floor.