Any chance you can just continue with your far superior breastmilk, even if you pump? It is estimated that there are over 100 nutrients in breastmilk that science is still trying to identify. Before you decide to switch, you may want to Google "rocket fuel found in infant formula" and "BPA in infant formula."
Last year Good Start got slapped with a fine for false advertising and some expensive, neonatal formula got recalled as well (this is from the CDC):
"A recent study concluded that powdered infant formula can cause serious illness or death in infants. The infants are typically diagnosed with Meningitis,Salmonella, Sepsis or Bacteraemia. These illnesses can often lead to brain damage or death. Powdered infant formula can be contaminated with harmful bacteria during the manufacturing process or contaminated if not handled properly. Doctors often diagnose the illness as Meningitis, Salmonella, Sepsis, or Bacteraemia." http://www.cdc.gov/mmwR/preview/mmwrhtml/mm5114a1.htm
Someone even mentioned Goat's milk rather than formula (I have no idea on that one, but it is worth checking into). If it is possible, then that is a way to supplement in a chemical free manner.
Good luck!
:)