Hi Susan,

An unfilled tumbled travertine or canterra stone would work nicely, or the surface of regular travertine could machined with a large walk-behind grinder on-site to create a texture similar to that of canterra pavers.

There are also slip-resistant products that can be applied to stone to increase traction. (I've used some indoors but believe some are also rated for exterior use)

Steve

Hi Susan, I have seen this tile called Antico Series Porcelain Tile. The tiles come in a few different sizes. The 12×24 and 12×12 size comes in a matte and rough textured finish, here is the link to see pics of travertine look tile: http://tiledaily.com/2012/08/06/antico-series-travertine-porcelain-tile-2-shades