Have you considered just using stainless steel sheet. I have done this in three properties. It looks good and is relatively cheap. I have details of a supplier that I have used in each case if you need it.

Try a slim porcelain sheet in a concrete look finish. The large format size means you'll probably need only one, so there'll be no grout lines. Have a look here, at the Portland 3.0. I think the Kerlite range also does a concrete look and is larger, at 3m long. The other advantage of a porcelain tile over actual concrete, is that you just wipe it down. Concrete is porous and will stain.

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

Hi Mimi, Your stone (probably Marble or Reconstituted stone as these can be damaged by acids) has been factory finished by diamond polishing to get the gloss level it has. A sealer will only help protect that factory finish and unfortunately it will not bring it back. The bad news is it is not possible to repair and so removal and replacement is the only real fix. This may be covered if you have Accidental House Insurance, but other than this, I am afraid there is no easy fix, sorry. Hope this helps though, Malcolm.