Nothing is going to "coordinate" but a plain flooring, and you need to go tile shopping locally and bring home samples..

Reinforce how? What is beneath the bath? Another living floor? A basement? Have you had a structural engineer? Did you heat the floor?Are you certain that shower is waterproof, and there is no seep to the bathroom floor?

Yes, another living floor. thr floor is heated, so it will likely get ruined when they rip up the marble. shower is waterproof. crack is due to seam in plywood of subfloor which shouldve had another layer.

The floor cracked from the heat, I would guess, turned on too soon following install of the marble. I doubt a seam in plywood would cause cracking, a sagging joist and a floor with movement would.

It's more likely the heat in combination with the marble. I'd wait at least a full month.......a lesson already learned by client who did not heed the advice

Thoughts on what to replave with? white porcelain? 12x24?

I would consider doing a floor in a more solid looking gray toned that matches the over all veining of the wall. It will look intentional against the shower walls and the tub.

I would go more gray than white.....all white? That will never be as forgiving, and will be harder to find as well. You're used to a lot of pattern which disguises quite a bit: ) of daily grunge.

PS..... what size was the former? that might be part of the crack issue as well.

former was 12x24. worth considering just a smaller format marble? what would yoi do?

I do not think the heat was the issue but you need to have avery solid subfloor with no flex to install 12 x24 tile and for sure marble . Get a nice 12 x24 plain porcealin tile that is a match to one of the colors in the marble and a matching grout .

Unless it is the SAME marble, you still need a plain. Even a smaller format in what you have, is no guarantee of a similar look when you reduce size. You'd need what is currently available from Mother Earth and major sampling on site with a few full boxes.

Chispa do you have a picture of the finished product?