based on the drawing, the wall where the bed is. HOWEVER, you mentioned that this drawing is not a true depiction of the furniture you will use and the wallpaper. if that is the case, i think the wall paper can work on either wall, it all depends on how busy this wallpaper is and how "plain" the bed is. if you go with a busy wallpaper behind the bed, you may want to keep your bed and bedding on the minimal side so that there is a good visual balance to the overall composition. if you go with snazzier bedroom furniture, then a busy wallpaper may be a bit much and you may want to put it on the other wall or use a textural option to serve as the bed's background rather then another focal point.

First of all, you should change the door swing from Left hand to Right hand, so you walk into a room not the wall. Put the bed where the dresser is now and the dresser on the other wall. Other then that there is not much room to do anything, or replace the window, insulate a wall and leave everything as is. Good luck

Kind of funny really how many people would feel exposed and would not want to use the bathroom. The more I think about it, it's a bit like a public restroom with stalls (as stall walls rarely go to the ceiling or floor and have the added issues of gaps between the wall panels and doors -- which thankfully we won't have!). Regarding the humidity control issue, I should have clarified this is only for a toilet and small hand basin (not a full bathroom with shower). The main room on the other side of the proposed toilet is our dog whelping room where we will have young litters of puppies (when we have them). Further down the hall, removed from this room, is our training room where there are likely to be other visitors but the proposed bathroom would be quite removed from that area. It would be wonderful to find more windows like the ones that are up near the ceiling! That would certainly solve the issue. I'll have to scour the demolition/restoration places.

Thanks very much for all your feedback. Just to answer a few queries - the deck is directly outside the main room so the new doors open out onto it. The doors won't be French - they're just the only doors that the 3D planner I'm using had, they'll actually be large stacking doors. I've had another idea too which would be a lot more expensive but offers a completely different approach. This is quite rushed so doesn't show accurate layout of kitchen or anything like that, basically just provides an idea. Thoughts!?