I am confused about the floor question. Is there not tile on the floor in the pic with the toilet? If not, you may not have a lot of choice. Because you did not order it before the job started, you will have to settle for whatever you can find in stock. I would go with a light to medium gray, since the vanity is dark.

For the mirror, I would stick to a rectangular one. Adding curves to this crisp, modern look does not appeal to me. I would go with the pattern you established with the shower and get a matte black framed one.

In cases like yours ….a patterned floor tile…with a little black in the pattern …..will tie in with the black touches and dark cabinetry….while adding some pretty detail…

2021 post..🤷🏻