Marble is a beautiful stone. You will need to have it sealed regularly (every 12-18 months and unfortunately if you're a keen cook you should be warned that it can stain and acidic things like lemon juice and vinegar need to be wiped up immediately. I say this as if you're anything like me you tend to share a lot of your cooking with your splashback. The alternative would be to look for a caesarstone type material in a marble pattern - Caesarstone and similar products don't need sealing, aren't porous and are more stain resistant. Good luck.

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.

The tiles from Johnson in the UK are stunning. It appears they only come in large 30x30 ? I was thinking of doing some sort of tile art just in the middle of the backsplash with the rest just plain offwhite tile. However, with this large 30x30 art work, the background tile would have to be cut to size to fit the area I have and might look too choppy???

I think that it will look too busy with the contrasting cabinetwork and the patterned tile on the floor. But then Australian tastes and styles in kitchens tend to be cleaner and more understated than our American cousins. I would keep it simpler, with a plain large format tile to make cleaning easier and to visually expand the space. Your current tile is very busy and probably hides grease splatters very well. Best of luck with your considerations, Dr Retro of Dr Retro House Calls