A "lazy sucker" (

that sounds soooo funny) makes sense. I am very surprised that a midwife would tell you to supplement w/o telling you how. You still didn't say on average how much weight she is gaining. . .less than 1/4 oz. per day? And what charts are we basing them on? Standard or bf babies. And does she have enough wet diapers? Oh and you don't have any of hte other issues. . .like you're eating enough/drinking enough, NOT on birth control, not pumping, etc. Oh. . .and are the lc's IBCLC certified? If they are not I would get a 2nd opinion from an IBCLC certified one.
My first inclination is that if she has enough wet diapers. . .I would start pushing for other testing to determine a possible medical cause. . .If she's peeing enough. . .she's getting something and that's a big clue as to what's going on. Another thing that I would try for awhile is to feed only on one side for 12 to 24 hours at a time. I am wondering if you have too much fore milk. That's not a terribly common problem but it can happen. . .especially with a lazy baby.
As far as supplementing, are you using a bottle? I would stop if possible. Supplmenet via an eye dropper or a supplemental nutrition system. I would only supplement on top of a feed. So feed and then offer formula.
btw, the fussy times you mentioned are pretty normal times to be fussy. . .wouldn't make me think she wasn't getting enough in and of itself.
Oh and btw--you ARE doing great! Sometimes these babies just come with quirks!
