There are thousands of 12 x 24 porcelain tiles that could work in that space. Go to a local tile store (not big box store) and find something that works. I would keep it simple due to your busy floor.

@chispa - Would we run them vertical or horizontal?

What exactly are you referring to so I will know?

Agree with @User why the shower pan?

https://www.schluter.com/schluter-us/en_US/Shower-System/Shower-&-Tub-Kits/Schluter®-KERDI-SHOWER-KIT/p/KERDI_SHOWER-KIT

I can't speak to the shower waterproofing method that doesn't appear to be visible in that photo, but with the "star of the room" being the floor, I'd choose a perfectly plain, larger format white tile to match the shower pan and white background of the floor tile with a matching grout (a big no to contrasting dark grout). I wouldn't lay the tile vertically since that's a more modern style and you've got that very rustic vanity which seems to be the discordant note in the bathroom. There's a vessel sink and minimalist, modern faucet...a sleek, slab door cabinet, perhaps wall mounted, may have been a more pleasing choice.

Do you have more of your floor tile? Can you get more? If so, I'd do the rear wall with the same tile, and then pick a white porcelain 12 x 24 for the other two walls. Given your rustic vanity, I'd hang the 12 x 24's horizontally in an offset pattern.

Here's a photo with the floor and accent tile the same:

Master bathroom · More Info

@Lyn - Agreed and I have no idea what that was done. I hate it.

@Sabrina - Yes, we do have additional of the star tile.

IMO that floor is enough of thet tile so a simple white 12 x24 tile for shower walls would be my choice but that whole space needs to be waterproffed and IMO domne before adding the pan. I thnk the counter next to the sink should aslo have a lot of water proofinf done before you use that sink . A diiferent waterproofing of course . The next time before installing anything in a space have a plan for the whole space .

@Patricia - From what I was told, the whole space was waterproofed before doing any work. I agree with a plain white tile.

" From what I was told, the whole space was waterproofed before doing any work "

How? Cement board waterproofing would be topical, and none is showing?

I didn’t mean in the shower area. That still has to be done.