Thanks for posting!! It sounds like you have a lot of the same pieces of furniture that we used in Alisha’s room, so if you would like a layout like hers, you can check out the floorplan we used here and try to replicate it! Depending on the placements of your windows, which sounds a little different than hers, you could possibly shift the floorplan over to keep the same flow!
As far as the marble walls, if you can’t apply wallpaper, could you paint it on a wall? It would definitely be a project, but I have a marble painting tutorial that we used on the surfboard from Eva’s room that could work on a bigger space as well!