I'd definitely put some kind of stone on the walls, all the way to the ceiling. I think the gas fireplace that you have is really cute, but might look at a stone slab on the floor instead of the mat that is there now. I'd take stone inside of that alcove as well, whether matching or contrasting. You can still hang art above, on top of the stone. It would really make the room!

Any of these wood work, you can also pick your color and have them mix the percentage of tint lighter if you find one you like

I have a dilemma with wallpaper. There is a 3 seater dark navy sofa with matching chaired, a wooden fireplace surround and a bay window in the room. The fireplace and skirting boards are going to be painted cream. I don't know what wallpaper to put on the fireplace wall to warm up the room a bit. Main colour scheme is silvery grey paint, very dark couch and chairs and black. Photos attached.

I think black, cream and gold is quite a classic combination unless you wanted more colour? Perhaps a side table or low console to the right of the fire but keep the profile lower than the fire. I would change the mirror for a larger one and add something tallish on the LHS, agree re painting skirts, would do these in the ŵall colour though to maximise ŵall height and also paint the door. Perhaps a glass coffee table with a rug under the sofas? I would keep the rug similar in tone to the floor. You could also try arranging cushions either 2/3 on one side with just one on the other to move away from a traditonal look but do bring in the gold and pattern. You could try just a grasscloth on the fire ŵall. I would also add art. If you choose black frames keep the frame fairly thin. Also agree re tv unit.