When the baby quits suckling, the body (pituitary gland, I think) takes that as a hint to quit producing (as much) milk. He's probably having a growth spurt about now, anyway; so if you were exclusively breastfeeding, he'd be wanting to nurse every little bit (which would alert your body to MAKE MORE MILK!) Since you're supplementing, he can get as much as he wants from the bottle each time. It should go pretty easily for you. Even if you (still) breastfeed him only one or two feedings a day, though, your breasts will make a little milk each day and that would be good for you both (like early a.m. and 12 hrs later at his bedtime).
Good luck!
(P.S. I'm 51 and nursed 4 babies for at least a year each, so have a little experience! LOL) I don't know (scientifically) about the cabbage leaves, but I'd assume that they're simply 'cool' and soothing and LARGE enough to cover the entire breast (and also waterproof if you leak. he he). Like someone said, breastfeeding is NOT an 'all or nothing' proposition. I started giving our kids juice and formula very early (they used to recommend starting juice and cereal at 6 WEEKS, not months!) and I always had plenty of milk.