My girlfriend and I are both non-op transsexuals; (i.e., she's MtF, I'm FtM, and we haven't had "the surgery" and don't intend to.) On a visit with her a little while ago, she and I were sitting in her car and talking about our feelings regarding sex. When our relationship started over a year ago she asked me to wait, which I was fine with, but didn't know she had been open to what we considered "in between" kind of stuff like oral (she doesn't want to go "all the way" because she was raped a little while before I met her and she feels like penetrating me is putting me in her position--it isn't, but I'm not going to pressure her), and while we had been discussing it we realized we were both in the mood and I asked her if she wanted to find some place more private and explore, and she said "only if you want to." I did.
Before we got started, I asked her if she still wanted to continue and if she had any other boundaries she wanted to set in place, and she said no. I reminded her that if she wanted me to stop at any time she could say so and I would stop everything.