styrofoam covered with fabric wall art. My daughter and I did this for her room. We used cheap painter canvas and scrapbook paper. We sprayed adhesive glue to the canvas and layed the scrapbook paper on top.
Hang some DIY crates on the area over the toilet to add some decor. The dried beach dahlias in tiny bubble vases, mason jars filled with candles & bath salts, some driftwood, and a few starfish & shells make your bathroom super fantastic.