We had 2 bathrooms with only a shower in each and we wanted to put in a tub and a steam shower. Not sure how I did it, but we managed to do that in the same overall footprint. Nice thing about small is that your money can go farther. We used pebble tile on the floor and Port Orford cedar (sort of reclaimed) on the walls. The cedar is light and we used a lighter color pebble tile, so the rooms do not feel dark. One has a porthole to a water view, the other had no outside light. We installed a porthole through to the other bathroom to capture the view, without compromising privacy. We also installed a porthole to the adjacent bedroom. We installed a steam shower in one that comes as sort of a contained pod (same with whirlpool tub in the other). The tub has a curved footprint that makes it look smaller than it is. We used a floating vanity in that bathroom and a more traditional vanity cabinet in the other. Don't have a pic yet, but the outcome is really nice. They are on a houseboat, so nautical makes sense, but cedar (similar to what is used in saunas) can relate to the mountains or woods just as well. In summary, I would say go top shelf on finishes, lighter in color (except our vanities are dark) and simple, borrow light or views from other rooms (your "windows" can be cheap as they are interior).