I can understand your concern from your detailed question.
Similac neosure is good as a follow on formula for premies when they reach about 2 kg weight,to give them good calories and protein for catch up growth.
If the baby is vomiting
all the formula feed s that you mentioned it may because she is used to breastmilk.-and hence will take time to adjust.soyamilk is given in specific conditions like milk protein allergy-so no need to use it without specific indication.[nido is to be used for older children(nido junior)after 18months of age.you take plenty f fluids,milkmetc for enhancing your milk supply.expresses breast milk and storing it when you are not available is the ideal solution at least up to 6 months in your baby.what about Nan formula.Did you try?All the best