Another bath inside whower idea: factory window shower - the BEST idea! Imagine this done huge-Japanese-bathroom style with an old claw-foot tub in an oversized shower, so you could have overflowy baths in a shower the size of a small room.
10 Ways to Squeeze a Little Extra Storage Out of a Small Bathroom Don't neglect the space above your toilet. This is a great spot for a cabinet, some shelves, or maybe just a basket for toiletries or reading materials. Image from My Fabuless Life.