My partner and I have had to do some adjusting around this as I've begun to transition. I don't have a problem occasionally using my boy parts for penetrative sex, but it's definitely not my favorite thing to do.
Rest assured that there are lots and lots of ways to please your female partner that don't involve penetration. Giving cunnilingus is probably the most enjoyable thing there is to do in bed, and if she likes penetration, there's no reason you can't do just as much with a sex toy as you can with the real thing--to be honest, a real penis can't really hold a candle to a well designed vibrator, as much as men would like to pretend otherwise

On the receiving end, I've discovered that being penetrated with a toy is lots of fun, and treating my penis more like a clitoris generally gets me going much more.
One thing to consider is that while issues of dominance and submission tend to creep into heterosexual sex (and probably gay male sex too, though I really don't know much about that), female on female sex can be a lot more mutual. It can be about sharing something special and not so much about one person taking control. Not to say that lots of lesbians aren't into Dom and sub roles, but if you take some time to reconnect with yourself there may be a way to understand sex without there having to be a top and a bottom. Being active and pleasing your partner doesn't have to mean you're being "dominant" and receiving and being pleased doesn't have to mean you're being "submissive."
Just my 2 cents.