One design tool that I think always makes a bathroom seem larger is to tile all the way up to the ceiling, and even on the ceiling if you are feeling it. I would even consider doing the same tile on the floor. It's very easy on the eyes and doesn't force them to stop and adjust, therefore making the space appear larger. Just think about smooth transitions and creating the illusion of one continuous space.

https://www.houzz.com/magazine/8-tips-for-creating-your-own-wetroom-stsetivw-vs~292118

https://www.houzz.com/magazine/bath-style-ready-to-try-a-larger-tile-stsetivw-vs~287768

In addition to what Annie said, you might also consider having rectangular tiles installed in a vertical orientation rather than horizontal...
...the vertical groutlines will visually extend the room making it appear higher.
I would also suggest having a rain shower head installed in the ceiling rather than a wall mounted fixture.