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.
add wood wallpaper to the kick plates of the stairs. Those rolls are expensive but you would only need one. Not practical with white treads though, it will be stuffed up from black shoe soles in no time.