I love your posing dog! As you have said you don't want to paint or change the furniture it's going to be very difficult to lift it. I see almost too much of the blue and it's also reflected in your mantel mirror. There are a few things you could try. Brighter book colours might lift it, they are very tonal. Also some multicoloured cushions would change the look and I would definitely look for a much bigger brighter rug. You could also add natural wood in the form of a large coffee table in front of the sofa. A brilliant green tall plant would also add a bit of contrast. I know you don't want to repaint but a briliant white gloss for the bookshelves would lift the whole room. I think a circular mirror over the fireplace would work better. Large with a simple frame.

The room is gorgeous and I love the window and the fireplace. I know you don’t want to re-paint the walls but I think the teal wall colour is a bit bright. It doesn’t suit the rest of the room I feel. The room has a traditional vibe but the wall colour is very modern. You could go for a more muted teal like Oval Room Blue by F&B, first picture or others from Dulux.

There’s a lot to love about your room… it has a very cosy family vibe and your dog is adorable. Your rug is a great choice in terms of colours but unfortunately seems a bit on the small side. Finding the perfect rug can be painful… I might try first trying to drawing out more of the yellow/mustard warm tones in it and your paintings. Maybe work in some subtle gold/brass accents… change the cupboard knobs, some of the picture frames and pots; add in a new floor planter, gold-bordered matts in your large framed posters, etc. Your mirror is lovely, but the heavy ornate frame does contrast with the rest of room’s style. A sleeker, simpler frame might be better.

What you have done is lovely, it just needs tweaking.
How about placing one large, or two flat weave rugs in Aqua underneath your existing rug, which would soften the impact of the teal walls.
Paint behind shelves in aqua, the graduation of one colour always help to tie a scheme together.
Could you gather objects in groups on the shelves, in threes and in different heights and leave some breathing spaces between? (There are tutorials on this subject!) Search for a few vases/ornaments in key colours.
An different style armchair together with your little side tables in the bay window could be a Reading Nook, would make the room feel larger. A patterned one with some ochre/yellow and a plain cushion would warm up the room.
Agree about the mirror, large, round and gold/brass would liven and warm up the room, the width of fireplace if possible.
As others have commented, wood and metal (natural) elements help to ground a room.
I think you are nearly there…well done!

I agree with the comment above about swapping out the rug and the mirror, I also agree with the comment about changing the wall colours I think something like the colours above would suit the room so much more and maybe add gold furnishing if you were to change the walls