Well done on your progress so far, a lot of people find it helps to swim a longer distance in the pool by using some recovery legs of breast stroke. you could start with every fifth.
This way you can build your stamina whilst getting some recovery without stopping.
64 lengths of a pool non stop can be long mentally and physically when you start, so its good to use the breast stroke lengths as markers. Once you have completed that a few times move to every 6 lengths breast stroke and so on until you are swimming the whole mile.