From one of the pictures i can see what looks like a vein cut travertine on the floor. I would start my design around a tumbled travertine 4x4 in a neutral color. Lay one row of the 4x4's at the bottom. Install a thin travertine pencil molding above the 4x4's and then finish to the cabinets with a tumbled 1x2 travertine mosaic. Stores like The Tile Shop can put this together for you easily and quickly.

Here's what the floor looks like

Many of the pros here will tell you that because you have the 4 inch backsplash as part of your countertop, you should not put up another one. If you want one anyway, go with something that is not busy - so probably not one of those busy mosaics - and probably not gray. Cool grays and warm toned woods tend to look drab together.

I have not worked with them, but there are advertised some stick on tiles that can be removed by heating up with a hair dryer. These could give you a backsplash that would be removable should you ever want to get new countertops. There is nothing wrong with your countertops, but backsplash comes last. If you think down the road you want a quartz or granite, you will want to wait with the backsplash, or try the removable kind. One thing about the so called removable tiles - they are more expensive than basic subway tile. Some of them mimic glass subway which might be a pretty look with your cabinets.

This is my backsplash. I had counters like yours and did not do a backsplash until I got my present counters 6 months ago. Then I put in the tile.

https://www.houzz.com/photos/my-pics-work-in-progress-phvw-vp~57088087

cute kitchen. do you have any plans, ever, on replacing the countertop?? If you do, you may run the chance of ruining the bottom row of whatever backsplash you choose. Sometimes they can save it, sometimes not. With that small backsplash you have now, it might be an issue if you bring the new splash down on top of it.

The distance between the countertop and the upper cabinets looks a bit low (may be just the photos). Do you know what it is? You could always raise those uppers a bit.

Thanks for the comments everyone. This was extremely helpful.

I didn't even think about how it might look strange to put a backsplash above the small existing backsplash. And after looking at countless pictures, I'm starting to think I'm going to save my money on the backsplash and put it towards getting new countertops first.