Hi Hannah! Wow I love the kitchen! I wish I had seen this earlier so I could suggest but I love the grey tile, it looks like a successful choice! You could add a marble cheese board to the island. The grey streaky tones In the board will probably tie in everything else. You could then put a terrarium on top of the marble board!

I suppose the question is "What are you going to do with the untiled wall?". Will it just be painted plasterboard? If you do decide to just go with the 200mm tiled splashback you will need to be very careful with your tile selection with the sizing and how the edge of tile looks. You should probably select a 200mm tile, as you don't want a cut, half tile in the space between the window sill and benchtop. Some glazed, ceramic tiles also have messy edges, so make sure that your tile selection looks as good from the edge, not just the front, as you will be looking down on the top edge of the tile. Or allow for a tiling edge strip to conceal the edge, but these always make the space look visually busier. With so much happening in your kitchen with the open shelves etc, I would suggest a plainish, neutral tile and tile up to the ceiling for a cleaner, more streamlined look, that doesn't need maintenance and repainting in ten years time. Open shelves often look better against tiles. By tiling to the ceiling there is no exposed tile edge to look messy, which gives you a wider choice of tiles. Best of luck, Dr Retro of Dr Retro House Calls

Sorry didn't finish my post, but I think the marble would work the best

can you post pictures of your kitchen and a floorplan. Base cabinets are usually 600 deep and wall cabinets 300 so your shelves would be a good fit at 300