There are many fake marble looking porcelain tiles so not sure what you are wanting from us. . I use 12 x24 porcelain tile almost always in bathrooms Often no pattren on the tile and I use that same tile for bathroom floor and shower walls and just same but smaller for shower floor. The color or pattern of the tile is a personl choice but the simpler the tile the longer you will love it . If that is keptsimple then down the road a change in wall color or accressories is simple . Remember the marble look yiles can look busy when done on a whole floor or all shower walls so my advice buy a box and lay them out in your space and see how it looks

Lowe's offers an affordable gray veined white tile. If you have a store nearby, you can see it in person.

I have also had great luck with Wayfair, never a broken tile delivered.

Many other options elsewhere, all depends on the budget.

https://www.lowes.com/pd/Satori-Statuario-Polished-Porcelain-Common-Actual-23-62-in-x-11-81-in/1002802304?store=&cm_mmc=shp--b--prd--pro--ggl--PLA_FLR000_PRO--1002802304--online--0--0&gclsrc=aw.ds&gad_source=1&gad_campaignid=21001526106&gbraid=0AAAAAD2B2W_2-cvbmt527d_Va7w2X0S8e&gclid=EAIaIQobChMIntyih5yakQMVW5buAR0vujv5EAQYAiABEgIQT_D_BwE