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.

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This is ours, standard upstand and large piece of quartz behind the cooker. In hindsight, and if budget allowed, we would have the upstand higher up like your image, perhaps to the bottom of our wall cupboards. We find the cooker splashed onto the paint as does the sink. We used the same paint as we have elsewhere in the house which you can normally wipe down but for some reason the finish on the kitchen means we have real trouble doing this, so we’ll have to repaint periodically.

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