Seriously, don't mess around with the breasts, the breasts look like they do because of the top half of the torso being far too tall, so try what I said, see how it comes out and post it even if you don't like the result.  You mentioned, ah, that's because she's so thin.  But that's largely where your problem lies when you think about this stuff.  Fact is, she might not be as thin as you think she is, because is if you shorten the top half of the torso, it will do more than you think :

• It will make her shorter (shortening something without scaling the rest will make it look fatter).
• It will change the plane on which her breasts lie, from being vertical to being partly horizontal, which is how they should be (see second from right).
• It will make her ass look better in side profile (even though it didn't involve editing her ass at all).

You're too preoccupied with all that perfect face stuff, and trying to do everything the perfect number of heads high etc, and this is what happens if you do things like that, like you said, about not seeing the forest for the trees.  It's ok to use that stuff as a guide I suppose, but personally I don't, cause at the end of the day, I wouldn't want to create something that isn't what I had in my head, and humans and their proportions are so varied that you could completely throw that drawing guide stuff out of the window if you wanted - you've seen enough nudes to know what a nicely shaped woman looks like, and it's those real women are the best guides.

Try what I said, and post it even if you don't like how it came out - consider that an order from ScareCrow :-D