1200mm or 4 feet would be ideal.

as a mum I agree worktop is priority, but also there's extreemly little cupboard storage so I would stick with the pantry cupboard and add a freestanding ikea Varde unit like attached pic ( I would have preferred integrated dishwasher too and a bit of moulding/ shape to the door style in a perfect world ) where's the fridge supposed to go?

We have Caesarstone in Misty Carrera on our island. It has a slight warm gray hue, which works well in our kitchen, and it's very durable against us and our kids.

Depending on functionality, how your island is used, it can be somewhere to showcase a different material, as in a traditional kitchen with a substantial timber top, or if it's a practical prep area, the durability and maintenance is of utmost importance. If it is a highly utilized work area the surface would be best suited to reconstituted stones, which are man made such as Caesarstone, essastone, quarel la etc, as natural stones such as granites and marbles are more porous and require some maintenance and care. Depending on form and style, your options are almost endless. Cntemporary spaces can indulge in stainless steel tops, acrylic solid surface tops that can be any thickness, profile and can actually be repaired without joints. Glass or concrete are more options. So you ask for help on choosing your island bench top, That is dependent on a great many things. Factor in how you would use is surface, and what you can afford, then think about the overall impact these options can provide on the entire space. Eliminate. And collect samples to make your decision. It will probably become the single most used space in the house.