I am trying to plan the same thing. We added a 2nd floor to our house and the bathroom upstairs will be for us and the kids (2 and 4). I am thinking of doing something grown up, but with cool colors. Like maybe small glass tile on the floor with enough grout that it's not slippery. And a cottage style vanity. That's as far as I've gotten! We will have a 1/2 bathroom in our bedroom that will be much more elegant. I just want it to be happier looking than traditional style, dark wood furniture vanities you see so much of. Good Luck!

In our bath, we went with a strip of the accent tile from the shower--this was something our builder was doing in his spec houses and we really liked it. This was great because I never really liked the marble thresholds to begin with--they never look right to me, they stick up too high posing a trip hazard and they are so cold. Raised transitions also tend to collect dirt along the edge that can be difficult to remove/sweep out. We used the accent tile transition technique at the doorways between the bedroom and the bath and the closet and the bath. Note that our transition was from carpet to tile in both. In our laundry, we did a very thin metal transition strip. Both transition options allowed us to keep the floor height at the transitions as level as possible reducing trip hazards and making the house more handicap accessible should the need ever arise. Here's a pic:

I think the key is a big mirror and overly-adequate lighting (an overhead light plus bright sconces). Shiny surfaces like tile or metallic wallpaper would also help. These aren't mine, but are all interesting small (windowless?) powder rooms: okay, this one has a window but its one of my favorite powder rooms ever! or you could embrace the dark and go for rich and cozy

The entire purpose of the site is to have collections of design photographs. Millions of photographs. https://www.houzz.com/photos/query/Gray-and-white-bathroom/nqrwns And the design fad is over, so you might want to look to your actual house‘s bones and style for clues as to what will have staying power and not look immediately dated and out of place.