Very nice room - not much needed, IMO. Love the rug and window shade, and chairs. If you are are good with plants, I would definitely bring in more plants -- ideally to the far side of the room, but that may mean only shade plants. I would style the bookshelves with more books, and large decorative items, for more impact. I'm not sure you need artwork in the room - I would add only if it is a piece you really love, as opposed to filling the space.

I would also change the floor lamp and side tables to something more contemporary (but that's MY taste, and may not be right for you.)

I would do a round leather ottoman, or wood - I think if it were the same upholstery as the chairs that would be boring. As for the wall, there are so many options. Depends on whether you like symmetry or not. For symmetry, six or nine small pictures lined up, or here are some other ideas:

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I would look for antique/antique style botanical prints.

For pillows, just about any color and print you like will work (coordinating with rug, but doesn’t have to match exactly). Etsy has a great selection.

Just examples of bringing great colors in:

For ottoman, something woven:

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Or something like a vintage Labarge coffee table:

Love this one from Ballard Designs … lots of fabric choices:

I think a large, solid coffee table or ottoman will make the furniture grouping appear cramped - and also obscure the pretty rug. If an ottoman is desired when reading, for example, I'd find a small one and stash it under the table to the left of the windows. Maybe something like: