Filling holes in travertine is not required really and if you get a quality stone (avoid online suppliers) then holes should be minimal.I was in the same boat a few months ago then we came across Arterra porcelain tile. I did a side by side comparison between Arterra Petra Beige and Ivory travertine and they look identical. The main reason why I’m going with porcelain is there maintenance free. No sealing or filling in holes with grout. I want to spent
my time enjoying the pool not working around it.