I'm in a similar situation. I live with my parents, and while I think they'll be reluctantly supportive, I can't risk being kicked out of the house. I think they're going to eventually say "well that explains a lot" but until I'm out on my own, I'm not going to chance any other reaction. I haven't been able to schedule an appointment with a therapist either to even get that started, but the new insurance policy at work, which will make it affordable, kicks in after the 1st of the year, so soon...
Anyway, I did find that there are a few things I can work on now to hopefully make my transition easier when I'm able to get started on it. I can work on my voice, which is probably going to be the hardest and "most telling" thing for me. I can also get myself in shape and just generally be more healthy, it's amazing what I let happen to my body because I just didn't care about it. Then there's other little things you can sort of "practice" if you want to call it that, like gestures, language pattern, etc. Things like that won't "give you away" outright, but they might make you feel like you're at least moving toward your goal. At least that's how I think about it so I don't go crazy.