Babies are born to be breastfed. And I think with some dedication from both of you, you can get your supply back up in no time.
You are right, bf is supply and demand. He needs to nurse as much a possible to get the message to you body that the milk factory is back up for business. Let him nurse as much as possible. And pump between feedings if you can stand it.
You are also probably right about the formula. Its different than what he was used to, and his tummy is probably adjusting. His belly will be happy to have your milk, again. :)
Try to avoid supplementing with formula if you can. You dont want to send mixed messages to your baby and to your body.
Drink lots of fluids. Water!! And eat right. Your body will be better able to produce if you are getting all the nutrients you need.
I hear you about the mother's milk tea. There are different brands, so if you dont like one, you may like another.
Also, oatmeal works. I dont know why. But, it does. Eat a couple bowls a day. You may notice an increase.
You can also use warm compresses on your breasts before feedings. And when you are getting to the end of one side, try a massaging technique. Slide your hand, with pressure from under your neck down to your areola, all around the breast you are nursing on. That will help squeeze out every last drop.
Best of luck to you.
And I commend you for your commitment to breastfeeding!!!