Your kitchen looks great. I think there are so many choices you could consider for your backsplash. But I think it also needs some warmth along with the texture you feel it needs. Once you get your choices sorted, look for some nice wooden pieces, maybe decorative cutting boards or bowls to put on the counter tops. Maybe some wood blinds on the windows, even if they are never closed and just sit at the top with a valance piece, it would add some colour and texture to the room.

Now for some tile suggestions......

Maybe some of these are going to be busier than you have in mind but I think your space can handle some pattern and your counter choice is not especially busy with large veining etc.

Most of these are marble mosaics and there are lot of choices with blue in them but you could easily go with marble with whites and greys, or grey to pick up the colour in the veining in your counters.

This first one is a favourite of mine....

This is Cloe by Bedrosians. It comes in other shapes and colours. Very pretty...they have grey and white too - worth looking at samples

I like the sheen on this one which is 4 X 4. I think this one is very pretty with the wavy texture, not just a plain white boring tile.