If you want info. on herbs/teas that will help produce milk and which hinder, try this book, "Mother Food: A Breastfeeding Diet Guide with Lactogenic Foods and Herbs - Build Milk Supply, Boost Immunity, Lift Depression, Detox, Lose Weight, Optimize a Baby's IQ, and Reduce Colic and Allergies," by Hilary Jacobson.
One of the nurses at Providence St Vincent in Portland recommends this book as the breastfeeding bible. I found it to be very informative and I didn't have to read it from cover to cover, I could scan through and find out which herbs like parsley hinders milk production if too much is eaten. You can definitely find out which foods to include in your diet and which to omit. It should help with which teas are safe and which are not.
Yerba Mate is not safe since it has a high stimulant. It is probably worse than black or green tea with their caffeine levels.
Lots of water and a snack around nursing time helps tremendously. You can get dehydrated from nursing and not keeping up you own fluids. Of late, Iiked a slice of lemon in some hot water. Very refreshing.
Happy nursing, don't get discouraged. Oh, and if you base your supply on how much you can pump; it is totally different than what your child actually gets. I could barely get anything when pumping, it got better the more I pumped, but never as much as my little one would take.
Good luck to you,