Personally, I would use a larger matte tile on the floor of the bathroom and stick with the 2x2 just on the wet floor. Stepping out of the shower onto a dry floor will not cause to you slip. It's when there is present moisture on the floor that you could slip. So the thought of having more grout joints in the shower for traction is more ideal. If you're still stuck on using 2x2 for the entire floor of the bathroom, I'm not going to fight you...it's your money and 2x2 is way more expensive than the larger format tiles. For grout, use an epoxy or single component grout. These grouts have built in sealers and are moisture proof. Cleaning of the products is as easy as using vinegar and water.

With those formal shapes on the floor and shower walls I wouldn't go free form on the niches. I would do 1-inch square glass tiles with some subtle color that references the floor. Or maybe see if you could cut the floor tiles to somehow work in the niches. Follow the lead of your inspiration rooms - you've got stunning floor and wall tiles- let them star and don't give them too much competition. Otherwise it starts to look too busy IMHO. Edited to add another option would be a solid color tile if you could find one matching one of the colors in the floor and a complimentary shape to the shower and floor. Free form circles just doesn't do it for me in your setting.

The granite is not shown. The large tile is a herring bone pattern on the floor. The shower walls are that same tile brick laid with 1/3 off set. The shower door is same color but with 1.5” squares. The accent wall in shower is the herringbone marble outlined with a natural stone that brings the two greys together. I don’t have a picture of it either. I think the pic makes the marble look cooler grey but it does have some warm grey in it also. I’m thinking of painting it agreeable grey sw.

So sorry for your experience with this! I have that exact same river rock on the shower floor in my basement bathroom, which happens to be used daily by my three teenaged sons, and when the shower base is done correctly it does indeed dry out completely.