Go for full tiles

You can use natural stone like marble for floor but do not use granite for floor at all as it is very slippery when wet. As for tiles do not go for glazed vitrified tiles for the floor for the same reason. ( floor becomes slippery once wet and may cause mishap) Go for ceramic anti skid tiles that are specially meant for bathroom floor. For wall tiles you can use whatever you like and then decide over the matching anti skid floor tile/ marble. Double charged vitrified tiles are usually used for flooring in rest of the house.

are their cheap yet attractive substitutes for tiles?

Anshu, You should share the images . You have gone for a bold choice with Grey and black in my guess it should look good with light pastel shades. Thanks Nitin Cornerstone Designs, Bangalore.