I'm with you. Travertine is beautiful but I'm not sure I'm willing to put it or natural stone in my masterbath. I have searched everywhere for a porcelain tile that knocks my socks off and I have found one that comes close. It's Mannington Carmel and I think I love it!
If you find it I would love to know what you think.

Here is a link that might be useful: Mannington Carmel

Emser has several travertine-like collections, depending on what kind of travertine you had in mind.

We used Casa Classica Vitality Series -- the different names are Earth, Wind, & Fire. Many people think that it is travertine. It's really lovely -- we used Wind and Earth for two different BR's. Here is the link to the website

Here is a link that might be useful: vitality tile

We used the tile linked below in the French/versaille pattern with 3 different tile sizes. We had several subcontractors doing work at the house when it was laid and they all thought it was real stone.

Here is a link that might be useful: Monocibec - Collection Graal, color Arras