I dated a transman for awhile and we got really sexual with each other. The most important thing is communication. Asking what they like and what they don't like, what they feel like they want, etc. The first time my partner had sex with anyone he did it with his clothes still on, it was the only way he was comfortable with someone touching him in places that triggered his dysphoria. Your partner needs to know that you love them and that you're willing to be very flexible and understanding about their needs. Establish trust and establish trust and establish even more trust.
I think it's great that you respect your partners wishes and I wish you the best of luck
