After looking on a few sites there seems to be batterys available for the superb with Different amp ratings.!

My question is, would it be OK to fit a battery with a higher amp rating than what I currently have fitted?

Yes. It will even make things better.

I fitted Bosch S5 096 - which is a fair bit higher rated than the Bosch S4 096 it replaced.  No issues and in fact car idles nicer - but the old battery was quite near the end of life.

 

I paid £83 for the Bosch S5 (cheapest was Eurocarparts click and collect via Ebay).  I imagine it will outlive the car.

 

For simplicity sake you just want to make sure it is the same size - which on my car at least is 096.