The first thing I want to say is good on you for getting as much BM as you can into your daughter.
You may be able to continue exactly what you are doing, and in 2 or 3 months her milk needs will actually decrease slightly as she begins to have other food - so in effect you end up replacing formula with food.

Otherwise feeding her more often may be the key - don't top up after every feed any more; instead, feed as often as you possibly can during the day (even if it ends up being hourly) and see if you can condense your top ups into a couple of larger bottle feeds (perhaps late evening and middle of the night).

"The breastfeeding mother's guide to making more milk" has been useful for some people around here too.

I also want to add that around now many Mums find that their babies act as though they are suddenly being starved. Keep doing what you are doing and that phase should pass - please don't assume that it is indicating that the supply you have is disappearing.