stone for roman bath.

Hi, I'm hoping that someone will give me some guidance about the correct choice of stone for a bathtub we are having made for our as yet to be constructed home?

We are looking at having an inslab heated 1.35m *2m roman tub created in concrete and then tiled. The tub will have two rainfall showers overhead and will be used very frequently for showering as well as for bathing in. Tumbled marble mosaic tile has been suggested to us as an appropriate stone for tub (both internaly and externally) as it won't have sharp edges and should be comfortable to lie on. I love the look of the marble and the feel of the tumbled stones that I have seen but I'm anxious that it would be the wrong choice for a bath and the veins unhygenic...mind you our builder pointed out that the roman's did in fact build their baths out of marble and they've lasted thousands of years! Can anyone reassure me about this choice? Thanks in advance for your help.

Lila