How about low, streamline shelves like these? You could also place some floor lamps or indoor tree plants on each side of the fireplace to balance the width of that wall with some height.

Nice room! Not a pro, but I think your original idea of built in bookcases could look really nice with the windows - just need to be in proportion.

I would look for bookshelves that are the same height as the top of the tile fireplace surround, and as wide as possible. Is the fireplace offset a little or is it symmetrical? If it's offset you could disguise it a little by putting a chair in the corner slightly in front of the bookshelf on the longer wall. With a tall reading lamp behind it.

It’s not uncommon for craftsman homes to have these.

You could build the bookshelves, just not floor to ceiling, and cover the windows with art. If you go that route then first cover the window with a black piece of fabric, so it will look nice from the outside and so that light won't shine through your artwork. Then just get some artwork big enough to cover the entire window. In fact, this is exactly what I did in my bathroom to cover a window there that I hated.

Love the example oaktonmom shared. I think that would look really lovely in your space. The glass doors keep things feeling decorative and really add character to that room.

What if you put the TV on the short wall across from the window? It looks like it might already be wired for cable there. That way you can put some lovely art over the fireplace.