How would you introduce formula for 6 week old?

So ive been breastfeeding and pumping but my supply is starting to lack now that shes eating more. I find she gets frustrated at the breast like nothing is coming out. I dont want to pump all the time as I just dont have the time for that. I would like to introduce formula and keep breastfeeding for comfort here and there. If you hVe experience with this please let me know your experience! No negatives comments please.