Then that’s actually what I would suggest, board-and-batten as in your pic above. It’s a perfect choice because it carries a theme from the rest of your house and is inexpensive to do. I shared an example elsewhere of what DH did to create a board-and-batten headboard in one of our cabin bedrooms and how he finished the bedroom walls in our casita the same way:
I did something similar with beadboard in a bathroom in our previous house:
Wallpaper above would have looked even better.