After lurking around this place for a while and struggling about how to talk to certain people I finally made the choice to come out. Communication in general is not really the easiest thing for me, but my coming out was surprisingly well received.
Starting with my mother (who also had the duty to tell my father)... it was half "okay, so my daughter may be my son one day" and half "you're a grown-up person, you have to find out what's best for you but make sure you know what could cause your issues". However, she had no problem with the fact that once I move out, I'll be living as a guy.
Next was my Biology teacher. Besides teaching one of my favourite subjects and generally being a nice person, he's also one of our "counselling" teachers and the one who helped me through various difficulties. His reaction was actually one of the best as he even told me about another guy like me who's been at our school until last year and about a teacher who has a transsexual son. This other teacher is known to be scary and strict but once you ask her, she'll actually be very happy to give you some advice. Maybe one of those "the world's smaller than one would expect"-cases.
Other than that, my chemistry teacher also knows - nothing fancy about this one. It actually rather slipped out due to the situation we were in, but she considered it an explanation for my absent behaviour during the last months.
The last one to know so far is my father. Besides realising that this explains a lot, he is also great when I need help regarding clothes and such - yes, those were one of my biggest issues and not being able to seek help openly was annoying.
In conclusion, almost everything went better than I've ever dreamed of and being able to talk more openly in at least some setting is one of the biggest relieves.
So... thank you for reading and my best wishes to everyone who still has to get through this :)