A belated THANK YOU to everyone who commented. This is the final result. We're super happy with it. Room A north facing "through-lounge" in a new build, 3 bed semi detached house Paint Walls: Purbeck Stone, Farrow & Ball Ceiling: Strong White, Farrow & Ball By the way, the room isn't as long and skinny as it looks in the photos. Painting it all one colour actually made it feel much, much larger. We were really impressed with the quality of advice the F&B staff gave us in regards to colour. We loved Purbeck Stone from the minute we saw it, and being brave really paid off.

Having looked at damask wallpapers in the photos on Houzz, on the whole if the curtains are a different colour to the wall then they are plain. If a different pattern is used in any soft furnishings then they are in the exact same colour as the wallpaper. I would think a stripe would go, as long as the background colour matches the wallpaper. However, it might be worth looking at some of the fabric and wallpaper designers websites or in a soft furnishings shop to see how they treat different patterns within the same colour collection. I suspect it will be to do with scale, ie put a small pattern against a big pattern. Another option is to use a sumptuous plain, such as a moiré and have a contrasting colour leading edge on the curtains which you then pick up in patterned cushions.

I like the curtain material, very pretty! I would suggest a striped wallpaper where one, or ideally both, of the colours matches the curtains or some other colour you already have in the room. If not striped, then some other strongly geometric pattern.

Thank you Sonia and Rachel! Sonia, those pictures are really helpful. I love the idea of velvet for the curtains, it makes a plain colour a bit more interesting. Thank you! Rachel, yes we wanted something really bold on one wall. It's quite a small area because we have a fairly low picture rail, and the bed will cover some of it. We're having two white floor-to-ceiling fitted wardrobes opposite, either side of a chimney breast, and we'll paint the walls a soft colour to match a shade in the paper. It's just this big bay window I'm not sure about - basically one whole wall is window and curtains (it's a typical master bedroom in a 1930s 3 bed semi). Plain seems boring but pattern will be difficult with the wallpaper...