I have seen glass tiles used in floors -- but I don't believe every glass is floor-rated. I'd call around to try to find one that is, or else maybe introduce a third material -- maybe a slate? In the shower, you could run your tile up toabout the 48" mark, then have an accent strip made of glass and tile pieces. There are so many different design possibilities! Look for some pieces called 'cigar rails' or 'half-rounds' to use as border strips. You can find them in glass and a variety of natural stones. You may also be able to mix a natural or man-made composite 'travertine' into a border and carry it off, even though your tile is ceramic. Another option would be metal tiles. Those could tie into your fixtures and hardware and be mixed with the glass as well.

I'm just trying to keep a more traditional look. My home is a 1920's brick bungalow. I've always thought I would keep the original hardwood floors and have a subway tile backsplash, but...the kitchen floor was in really bad shape. We were unable to save it and couldn't find 1-1/2" wide unfinished red oak strip flooring to match it (and the rest of the first floor), so we put in a slate/quartzite tile in instead. I'm still open to subway tile (and still love it), but frankly, I'm getting tired of seeing it everywhere and was trying to think of other options. I'm loving the hand-glazed tiles lately, maybe crackle glaze, in a 3x6 subway or 4-6" square. Also considering laying the square tile in a diamond pattern. Just trying to get my head around other ideas that would still be appropriate for my home. The floor is rather colorful, so I'd like to keep the backsplash simpler, but with some shine, to contrast with the matte counters and tile floor. I appreciate all your input.

Here is an option if you prefer the checkerboard design using 2 different tiles. I think they would work nicely. The Ebony Marble design is forgiving in colors used, not too black and solid. The white in it might be a soft white, not too white. Maybe samples would help. The size tiles and dimension thickness would have to be the same. I did not verify these. Ebony Marble https://www.lowes.com/pd/Style-Selections-1-piece-12-in-x-12-in-Ebony-Marble-Peel-and-Stick-Vinyl-Tile/999978538 The Crescendo might lean to an off-white. Crescendo https://www.lowes.com/pd/Armstrong-Flooring-Crescendo-12-in-x-12-in-Groutable-Marble-Look-Peel-and-Stick-Stone-Look-Commercial-Residential-Vinyl-Tile/1001435690

Yes. Draw out a cube (or separate walls) of that size. Then try placing 12 x24 squares on that wall. You are going to have one whole tile in the center of each short end and 6” wide pieces on either side, or a 1 ft piece on one end. Do you like that look? You will have 2 and a half tiles on the long side. If you switch the orientation of the tile and put the narrow side down, you will either need to have the walls widened by the space of two grout lines, or have one side of one tile cut just a tiny (likely jagged) bit. Make sure your tiler can cut those edges well, because, the tiles being so big, the jagged edges become very obvious. When you have a busier wall of smaller tiles, they do not stick out so much. Only if you make the shower exactly the size of the tiles, plus the grout, and lay them in a vertical stack, will you get rid of cut edges. Play with layouts and see what you like. You can also consider Corian or Swanstone and have a life-long beautiful shower wall with no grout. Anywhere. If you vacuum or sweep regularly, a black floor can be nice. That is, unless you ever use powder. If you do not clean your floors regularly now, do not think about a solid dark color for the floor. Floors are not wet all the time, so their grout should not discolor. You can have more grout lines on a room floor than in the shower, without mold or mildew.