I would suggest that you pick ONE boundary that you can draw with your husband. Not with yourself, or your own appearance, but something that just KILLS your self-esteem when you allow him to do it. Maybe it's the masturbation, maybe it's something smaller that you start with. Think about it ahead of time, think about what you'd like to say to him, and then visualize yourself saying it -- confidently! -- and ROLEPLAY IT, over and over again, even out loud (when he's not around, of course!) if you have to.
Then do it.
You will feel SO much better about yourself, he will gain respect for you, and you can then set a goal of a 2nd boundary that you can do thereafter.
Part of the problem of being a non-confrontational person (I know, cuz I AM one!) is that you rarely think -- at the time -- of what to say. Afterward, it's like you knock yourself on the head like Chris Farley in that SNL skit: "Idiot! Why did you SAY that!" Just like parenting, the best skills are planned out ahead of time, because after all, most of their behavior (kids AND spouses!) can easily be predicted, am I right?
So when he does or says "X", be prepared to do/say "Y."
