Slate tile is a great choice. I have it in a washroom and we love it. But it does tend to feel cold underfoot. Any chance you are considering under floor heating in that bathroom.

We got brushed slate, which means that there are no rough edges or shaling going on. We got a dark grey colour but I also saw it in other colours, lighter grey (almost a greige colour), a green colour and some that was closer to black but had some significant rust colour in it. If you have a look, you should find it easily and it came in many sizes as well. I like something like 12 X 18 or 12 X 24 tile for flooring.

When you say you want to use it in the shower as well, do you mean on the floor of the shower? If so, then you'd need much smaller tiles for that to accommodate the slope needed towards the drain in the floor. But you can likely find the same stone in smaller tile sizes.

I recommend the brushed slate for the smoothness. Some slate I looked at I felt the ridges were enough to catch your toe and some were quite sharp feeling as well.

I think that could look really fantastic with a white subway tile. Have a look at some of the handmade looking tiles. That might go really nicely with the rustic look of the slate tile for the floor.

Have you chosen a vanity? We went with a pearly grey colour and that was the colour of grout we used as well and it looks great.