Whilst we shouldn't have to hide things, it's a lot easier to not tell dis-believers about co-sleeping (don't worry, Santa won't be visiting your HV this Christmas if she doesn't believe!).
My son was very sicky as a newborn, he would bring up what seemed like a complete feed, then be head banging my chest as soon as I'd changed him for another feed. - BF babies feed as much as they need and if they take too much it's perfectly normal for them to bring some up - not wrong as your HV seems to think. My HV told me not to worry, they regulate their own intake, their bellies are the size of their fist, so they may well take too much sometimes - so unless you're holding his head in place and forcing the sucking action, i doubt very much you're feeding him too much. Sounds like she's not a HV who has breast-fed - anybody who can make a baby take a BF they don't want would be pretty inventive IMO .
and well done on the 12oz - how old is your LO? DS was sick for the first couple of months, usually twice a day, massive amounts, I was always convinced it was a full-feed, as he would then have another full-feed straight after emptying himself, so apart from being exhausting with the changing and having to give another BF, I wouldn't worry too much, sounds like you're doing really well! -
Don't forget to put your feet up with extra choc cake to compensate for the extra feeding