Great Post.
We are always getting asked about installing our u/f heating under Travertine, so this will add a little bit more to my knowledge.
We always add to our quotations; 'powder flexible self-levelling compound / powder flexible tile adhesive'.
Quick Guide from tfs:-
"There are many more areas where there may be additional requirements when installing travertine such as sub floor prep, under floor heating, new screeds etc."
"Choose a flexible adhesive and grout that is suitable for stone."