Any good porcelain mosaic with a .42 or greater DCOF rating would work. I use Daltile Keystones a lot. https://www.daltile.com/products/Mosaic/Keystones

If your walk in shower is of standard size, you can get solid shower bases made of various materials, from cast iron, to acrylic, to Corian to terrazzo.

I have a custom shower base made out of Corian and I think it probably worked out less expensive than tile overall because the labor was so much less.

Honestly I don't know that I would ever do a tile shower base again unless the shower was gigantic. If I were to, I would also probably use the Daltile Keystones. as well.

Subway tile in the shower will potentially be a "nightmare" to maintain. Why do you want all that grout?

My master shower has 30" x 30" porcelain tiles on the shower walls and my main guest bathroom has 24" x 24" porcelain tiles on the shower walls.