Quite a passionate exchange and probably no one fits all answer, all the more so as it is all about fit, isn't it ?
(my apologies for the pun! )
I have been in a similar situation to Joanna for over a year now with just one significant difference, I don't have big boobs, somewhere between A and B. I do however have shoulder lenght hair which I wear in a ponytail to work, beardless face and arms and far more feminine facial features than pretty well any guy of my age.
Also, even dressed male, (when traveling for example) I have been Madamed regularly by third parties in front of colleagues and I know from those that I have come out to, about ten people now, that lot's of people have asked questions about my gender.
All of that being said, what people notice most is the work I do, so, even if my appearance raises a few eyebrows, I have no reason to believe it has been a problem internally . Basically, people are mostly sensitive to change and the people I work with are now used to seeing an unusually feminine looking manager and probably only give any thought to it when a third party, who meets me for the first time, brings it to their attention again.
Regarding dress, I have also arrived at a stage where dressing as a guy is almost painful and I haven't bought a single item of mail clothing since 2011. In my place of work, standard is business casual to casual casual, very like what Joanna described.
I mostly dress at the casual, casual end of this spectrum wearing almost exclusively female clothing ie. jeans (Levi's demi curve, size 30, for me as I also have a few curves, especially my rear end..
), chinos, blouses (mixtures of cotton & silk for example) , woman's leather jacket, women's casual shoes etc..
Even with my smallish boobs I still avoid tight fitting blouses though as they would make even my breasts look too obvious and while I have clothes something like those in the picture above (closer fitting though), which in my opinion woud be very feminine with a little jewelry and nice shoes, I have not yet worn them to work. That will happen when I can finally come out to everyone and even then, I would consider that pretty formal, on par with suit shirt and tie for a guy.
So Joanna, while I believe you should at least come out to your boss very rapidly (I did that with mine one month after staring my new job), if you don't yet feel ready to come out to everyone, I think it is pretty easy to find sufficiently androgynous female to be able to dress comfortably and still maintain a minimum of stealth until you and/or your company are OK with making your status public.
Wishing you every success no matter what!
Hugs
Donna
