Either ask a countertop manufacturer to cut you a tiny strip of matching countertop. Or match the color in a subway tile. Until you can do the whole space.

Just a coordinating tile up 4” on back wall and install mirror above that.

I vote for no backsplash. I don’t care for the look of a short vanity backsplash. Have a faucet that reaches out into the sink and whose controls are not too close to the wall. Use thick paint on the wall like BM Regal Select in a pearl or semigloss sheen, then a thick bead of silicon caulk between the sink and wall.

If you splash around a lot and must have a backsplash, or if the vanity top pools water toward the wall, I would try to find a nice design that integrates the mirror and maybe rises up higher than a typical bathroom backsplash.

Another option is to tile the entire lower half of the wall and have the tile stop at the height where the 4” backsplash would stop. The tile would be like a wainscotting. You may even be able to find plastic/composite pieces that you can use as a substitute for wood wainscot, and paint them. They are waterproof, unlike wood and drywall, but I don’t know how the paint will hold up on the composite if it gets wet all the time.

It just depends how important the aesthetics are to you. If you are happy with a 4” backsplash, go for it.

Regarding the 3” gap, you will need to clean the floor and wall in that gap. Figure out what tools you will use, and if you can get your hand and arm in there to get all the way to the back. It will get dirty, probably more dirty than the rest of the bathroom depending on where you put the soap and hand towel. I prefer vanities that look more standalone for aesthetics, but the cleaning is more difficult.

Here is our shower tile (not yet grouted). Really torn still between the blue or grey for vanity backsplash

Oops here is the pic

I think @tsjmjh is on the right track. Here are some photos:

could you show each wall

Without seeing the room, I'm leaning towards the grey since the vanity is already navy. Too much navy on one side may start to feel unbalanced

There is nothing else to show yet, vanity is going in tomorrow

Still it's helpful because we may be able to tell you "add the grey in this one space too" or things like that. It's ok if you don't want to share tho. In that case, I'd do the grey

It’s finished!

looks great!

Hey Stacey, love how your bathroom turned out, Im actually looking at these same wall tiles from HD. Trying to find a ”white” bathtub to go with the tile. Do you know the brand/model of tub you used? Everything I like doesn't look like a true white.

I think it’s this one.

https://www.homedepot.ca/product/mirolin-sydney-5-ft-rectangular-left-hand-alcove-acrylic-non-whirpool-bathtub-in-white/1000479100

Our contractor got the tub for us

I‘ll have a look at this one. Thanks for your time!

Hi Stacey, my contractor is almost at the tiling stage. Struggling with grout color, light or dark. Can you tell me the color you used. Thanks again!

We used a light grey grout :)

Great, thanks again! You’ve been so helpful. So many decisions!