I realise you’ve tried different variations on the layout so have you tried putting your sofas at right angles to each other? With the two seater nearest the door, the three seater covering the fireplace and a coffee table between them. If you did this, could your tv then go on top of a low unit (with drawers!) on the other side of the bay window?

Yeh I've tried this. It just feels a bit off, as your facing the door. Feels like your waiting for someone to come into the room. Plus all the plugs and wiring etc are where the tv currently is so practically its not ideal. But I get why you'd suggest it 😁

have you tried the sofa in the bay so they.’re opposite each other with the tv where the fire was? Don’t centre them to the bay/wall but a bit closer to the entrance door and I’d pull them away from the wall/window a bit. You could then zone the seating area with a rug and have your curtains.

I like the green but have you considered painting the walls a stone colour? The ceiling would then be a shade or 2 lighter to give the room some height. I’d paint the radiator in the wall colour

If you like the location of the sofas, and just working with what you have - I'd move the recordplayer-drawers so it's on the wall to the right of the door (facing the fireplace-wall), then bring that 3-seater sofa forward a foot so it's not against the wall and move it slightly to the left so the little side table has a bit more space too. Move the guitar over to that wall too.

I think the art isn't right - the small bits are quite small and the large piece above fireplace should be something that is wider rather than longer - so I'd relocate that to somewhere else in the house and keep an eye out for something larger or 2 or 3 pieces that can be hung on that wall together to create a wide view and add some interest to the space. Or maybe try the big piece of art to the left of the fireplace and hung a little lower - it's too tall for the space above the fireplace.

To make the colours work better together you need something which contains the lilac and the blue - cushion/s, a throw for the footstool/sofa, a piece of art, a tray on the footstool - not all of these, but something more intentional. And it can be a lighter/darker shade of the colour, not the exact colour - and it can just be a small piece within a larger pattern that repeats the two main colours in the room. I think that's perhaps what you are thinking a rug and/or curtains could do - which would be possible, but I don't think you need a rug in the room and I'd try a couple of new cushions and a blanket first.

Curtains - you could do roman blinds to add some colour/softness - you'd need three and you should hang them as high as possible above the windows so they don't cover too much window (and it'll also make the room look taller with taller windows). Or get a curtain pole that goes all the way past the windows so the curtains can hang to the sides and not in front of the windows all the time - again, will make the windows look bigger and stop the light being blocked. I don't think curtains are the answer though and you have blinds already for privay and light control. One more thing would be to paint the radiator the same colour as the walls to make it disappear.