A.V.
we don't have travertine, but my guest bathroom floors and shower walls are done with tumbled marble - also very porous. the tile came from Lowe's and they sold a product that they told me to use on any natural stone - it does pretty well. i forget the brand name, and don't know where i have stored the cleaner at the moment (we are still building, so things get moved around by the day!), but it says on the jug, "Marble & Stone Cleaner"....it is a goldish brown plastic gallon sized container, rectangular in shape, with a built-in handle, not like a bucket. they still carry it at our Lowe's, in the tile section, never looked where they keep the other cleaners.
best to you!
A.