Do a search on Houzz for backsplash tiles to identify what you like. Then go to a good tile showroom (not the big box stores) to see them in person. The showrooms usually have sales people with some design ability on staff (it's hit or miss unless you go to a very upscale showroom like Artistic Tile, Walker Zanger, Ann Sacks, or Waterworks). They can help you.
But keep in mind that simple is best. Pick one tile for the walls and a complementary one on the floor, including the shower floor. Stick to porcelain or ceramic--they'll usually be less expensive than natural stone, and easier to care for. And find a line that has multiple coordinating tiles for ease of selection, since you are doing this yourself and have that religious aversion to hiring a designer.
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Not the mirrors but the shower.
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