D.W.
This is a question I would ask the doctor. I know you have to switch up when you quit nursing completely because the mini-pill is only effective (and it's not 100% unfortunately) while you are nursing so check the fine print with your doctor on that supplementation question.
And I don't know about all women but I weaned my daughter at 20 months, started on the regular pill and my milk was gone in a heartbeat! I'm glad I didn't take the regular pill while I was nursing her like they said I could! (slap to the forehead over stupid doc recommendation) Glad I was smart enough to do my research.