breast milk and formula......

Nicole • 💞ftm to beautiful baby girl💞

my baby girl is now 3 months, I pump and bottle feed but my milk is slowly decreasing to the point where I'm dipping into my freezer stash twice through out the day, I only have about 150 ounces left in the freezer and take about 9 ounces out a day. I would like to continue pumping for 3 more months but will probably have to start substituting a bottle or 2 a day with formula.... how do I go about doing that? I know nothing about formula