storing frozen milk

I need some ideas for storing breast milk. I have the medela pump and I pump into the bottles that came with the pump. My lo is 8 weeks and I go back to work in a month. I'm not sure how much she will need per feeding so I don't know what kind of increments to freeze the milk in. I like the idea of freezing the milk in ice cube trays and then only defrost what I need but the trays I ordered don't seem to be consistent with the amount they hold. They are supposed to be one ounce portions but when I poured five ounces of breast milk into the trays it filled seven compartments not five. : / just trying to figure that if the best more practical way to store the pumped milk.