There are a few different types that are one fits most.
You have the ones that need a cover such as Baby Beehinds or Mandy Mac. You just need to buy new covers as bub grows.
There are also pocket nappies that have adjusting snaps in the front. Bum Genius or Haute Pocket are a couple of types in that category.

The pocket style nappies don't have as good aborsbancy as the fitted ones nor do they contain runny poo as well. This is due to the cover being a better barrier.

Pockets are nice and trim though in comparison and the clothes fit over them better.