From experience, the baby will take the formula if it is hungry enough. With the breastmilk you have probably been feeding on demand whenever he wants it. Often times when doing that the baby is not actually "hungry" for a meal when the eat, they just want the breast or just want the breastmilk, but they are not HUNGRY. I would suggest that you try Enfamil. It does have the best nutrition value and is the closest to breastmilk. I would try that. Commit to feeding the baby a bottle of formula for whatever feeding you are wanting and just stick with it. If he will not take the formula, then she probably is not hungry, he is not accepting it because it is not the breastmilk that he desires. Put the bottle away and cuddle with the baby, read to the baby, keep her distracted as long as you can until she is fussing again about being hungry. Offer her the bottle of formula again. IF she doesn't take it that time distract her as long as you can and then reoffer. Eventually she will be hungry enough to take it. Notice, I did not say to let her cry or be upset until she takes it, just keep her distracted. She will take it eventually take it. If you think that she doesn't like the formula, one thing that I guarantee she will take is the liquid ready made formula that can be bought in cans or small individual feeding bottles. It is more expensive, but if money is not a problem try it. If you can't afford the ready to feed stuff, try the concentrate that you mix half concentrate liquid and half water. Both of those options taste better than the powder. They are much richer, milkier and sweeter tasting, much more like breastmilk. If you are just supplementing, it shouldn't be to much more of an expense to buy the good stuff.