One doesn't become transsexual. One is born transsexual.
Crossdressing can help one uncover for themselves that they are transsexual - as it did for me. It gets harder and harder for me to switch back to "being a guy". For myself I have realized that that guy I have such a hard time going back to being was a complete fabrication of mine that I created to protect my inner being from the pain of being a girl but everyone else insisting that I was a boy.
I wear mostly female clothes when I am not at work (and even then it is just what I wear on the outside).
My hair is past shoulder length so I never have worn wigs even though I bought one early on). I often run errands without make-up or forms wearing women's jeans and a top and still get called ma'am sometimes, sometimes sir. If I am wearing forms it is almost always ma'am. Sometimes even when I am working out in public, dressed as a dude, I have been called ma'am. Usually when someone sees me from behind or a side view.