If your state has employment protections for TG employees, I think you should consider asking your boss's help on not being called sir. Like, if I had been in your shoes at my last job (federal gov't, so pretty decent protections. Better for binary TS, but a long, long way from discriminate-freely practices being legal.) I wouldn't have hesitated to ask my boss. I don't think she would personally approve of me transitioning, but I have no doubt she would have looked out for me the same. Both because of the rules and, more importantly, her loyalty to her people.
You might not have to disclose to your boss, but if you had to, at least in theory, you would be legally protected from retaliation. A good boss knows how to respect sensitive parts of employees' personal lives.
Don't be hasty, think this through thoroughly with lots of input.
Does your job require customer contact? (Don't share the answer if you don't want to.) It's not really right, but I imagine employers worry more about personal presentation when you're part of the business's public face.
Now, yes, I was going to recommend therapy but not gender-therapy. Both as a compromise between you and your father, and because I think it would help you deal with the
significant conflicts in your life right now. (Understatement much?)
I suspect that an intersex diagnosis would help bring him around. I also would not, if at all possible, pin all your hopes on it though. It is very difficult for someone assigned M to get assigned F later. The good news is as an adult you have a right to refuse medical treatment, so the worst case horror I can imagine isn't going to happen.
("Why yes, those are real breast buds. Don't worry, we'll take them right out ." Oh
hell no.)
Another thing to bear in mind is, as far as medicine is concerned, yes, a male body can grow glandular breast tissue. So... I'm not sure a diagnosis would be automatically awesome. Pursue this course to learn the truth, not hoping for a bargaining chip.
Anyway, therapy. My opinion on socially-conservative queer-fixing "therapy:"
No. Please, God, no!Legitimate medicine agrees. At the same time, I think it would both be too much to ask of your father and perhaps not what you need to immediately go into gender therapy and transition. Don't get me wrong, you will get to transition, it's going to be awesome, and I want to do what I can to make that possible.
But you've grown up through some tough experiences. And there's a good chance that some of the things you've learned to survive should change. It isn't your fault and it's not at all like you're stuck the way you are, but my guess is you, like me, still have some growing up to sort out.
At the same time, I worry about a not-so-good gender therapy program thinking transition alone (maybe following a one-size-fits-all script) will heal your wounds. I disagree. Might be a good way to run a business, but not to help people.
So, my suggestion for a therapist: someone who's good with young adults.
Actually, if I could share one of my issues, maybe it'll help you get that conversation started.
I have an awful time trusting authority, and with appreciating and admiring my father the way I feel I should. It's likely that one cause of this distrust and misunderstanding isn't his fault at all. Over a period of five years I was verbally and emotionally abused by teachers at school. It was never violent or sexual, "only" humiliating, degrading, and manipulative. After two years I had developed a festering grudge against adults -- just about when my biological clock said it was time to become one myself.
This is one of the most important things I'm working through in therapy. It's not something I blame my father for, and it's something I can say "well, I'm working on this
awful experience."
If you can find something in your past that bothers you, isn't your father's fault, and isn't (primarily) a gender issue, I think you should use that as an in to therapy. Say "I really need to talk through X. I think it's holding back my growing up."
Therapy sessions are of course confidential. Once in,
do talk about gender and your father and whatever else bothers you.
Is it dishonest? Perhaps a little. But, ask why your father has to know all of your issues. You can't talk freely with him, can you?
Gosh, I hope this isn't too much to digest.