congratualtions on the birth of your baby elb1, but sorry to hear about your woes.
As far as I'm aware, babies are expected to lose about 10% of their birth weight, but provided they have regained their birth weight by two weeks old then there is usually nothing to worry about. your milk normally only comes in around day 3 so I'm really surprised your MW advised topping up quite so early on.
with regard to seeming to like the FF, of course she does....it's easy to get formula, but a little harder to get at BM. the head shaking and tossing I imagine (I'm no expert) is a result of nipple confusion from changing between BF and FF.
Re your big boobs.....I'm currently a 34H, so by no means small, and although I find it easier to feed at home with a cushion on my lap, I can manage to feed very discretely in public. It just takes a little bit of practice, and BF cafes/support groups are great for giving you the opportunity to hone this skill.
I hope that someone more knowledgeable comes along soon, like tiktok or hunkermunker, mears or moondog, but in the meantime, you are doing a fab job, and every brest feed you get into he is getting her off to the very best start in life. Although it is really difficult at the moment, if your latch is fine once she's on (try lansinoh on your nipples between feeds, tis fab stuff)
then it would be great for both your LO and you if you could persevere.
I would also second the views of getting some support via a BF counsellor or lactation consultant. If you want to BF, it is still possible to get to the position of exclusive BF, but equally, if you feel that it is not for you, then your DD has had a great start!
I hope this has made some sense.
Good Luck
Daisy xx