Just to offer a different view point. Your floor tiles look amazing. Why not flow the idea through and use tiles of that ilk as your splashblack. We have just recently finished a kitchen with a similar feel and our client opted for patterned wall tiles as their splashback. Based on your comment about the floor being chosen to banish boredom If you are worried about carrying through more of the same tones and want to inject colour, you could always do this through your accessories, that way if you fancy a change.... The colour tones you have chosen provide a great canvas on which to complement or have fun with colour.

At Lusso Stone we now offer splashbacks/ up-stands to clients with freestanding basins, we think this can help towards protecting paintwork ( if tiles are unavailable ). It seems to be working quite well as the stone resin material up-stand compliments the stone basins whilst making sure paint work stays well away from waster marks.

Depend on your water quality if it generate mildew often then avoid glass If you use tile avoid bright color grout cause it Will get yellowish or black after sometimes, bigger tile are better because less grout lines to clean Theres Wood called hinoki used in many Japanese onsen, it ressistant to rot, water, insect and has natural antibacterial property plus if in contact with hot water or steam it gives of therapeutic Woody smell https://share.google/Odjcre9a9hXgCmFPO

You don’t fave to have the same height all the way around the kitchen. You can have a 10cm upstand around most of it and then taller behind the hob. Personally I like the splashback behind the hob to be wide so make it the width of the shelves or the wall from the window to the corner and like Isla says make it the height of the shelf. Alternatively match its width to the wide cupboard and two small ones under the hob and then height size again shelf height or 30cm