mama you are doing great. I promise you won't regret continuing to nurse!!
That's awesome that he nursed from the breast well! It's important to work on latch with him to save yourself some nipple trauma. Here's a couple (non LLL) resources on latch and positioning.
Have you talked with your LC or your Dr about a plan to wean from supplements when everyone is happy with the weight gain and diaper output?
This is really exhausting for you! It won't be forever though, keep at it mama.