You can mix tile types. You need to be aware of the potentially varying tile thicknesses so that compensation can be made during install. They should be installed such that the top surfaces are level.

Oh i thought you would like to add different color tiles for your flooring.But it is ok. You can use mix the tile types according to your comfort.

I think using a darker tile border looks great! That said, I wouldn't change the type of tile (ceramic, slate, porcelain, marble, etc.) and as mentioned above, be sure to do a side by side comparison of the two to make sure they are the same thickness.

If you end up doing a border, you should consider using a diamond pattern in the center like in the picture below. In my opinion, it makes a space look more warm and inviting, as well as more custom, even though it doesn't cost a lot! It also breaks up a predictable pattern and makes the floor pop.

Here is a link that might be useful: