My partner is trans, and for now we still have penetrative sex (not as often as before, mind you.) I think a lot of us being able to continue doing that has been mindset. I recall trying to reassure her early on that, anatomy wise, she's currently in the best possible way to please and be pleased by another woman (because we currently fit like puzzle pieces) and she seems content being able to perform without any issues and is far more into it than I think she was before. I also am extremely mindful to treat her with utmost care and tenderness, which helps a lot. I know in the past her sexuality was marked by expression of dominance and aggression, so we are pretty much the opposite of it, and she is pleased to now be able to express modes that are far more fulfilling to her. I think (hope) that we just get caught up in our love and how into each other we are that everything else just kind of fades away. (We've never had any genital dysphoria issues yet.) I focus a lot on her perinium and below as a way to give her sensations that aren't so central to her current genitals, but in conjunction with. I also to my best to treat them the same way she treats mine.