I am going back to work next month. Ds will be 6 months. I've been expressing for the last couple of months so have a freezer full of breast milk. He has the odd formula bottle at the moment (1 a day) and the plan is to mix feed, and hopefully I can still breast feed him mornings and evenings. Is it better for him to have all expressed breast milk first? I didn't know if the benefits were any better if he has more over a shorter time or less over a longer time and I cant seem to find any information anywhere. Thanks in advance for any advice.