I has a similar issue, but then I realized that my partner doesn't see me the same way that I see myself. While to me all of my faults are visible, to him they aren't even remotely noticeable... Especially in the bedroom. Most partners will be the same way. Try to get that into your mindset.... Or, alternatively, buy some sexy lingerie that feels like you.
I recommend just talking to your partner about both of your fantasies. Some are really, really simple. If the role play isn't perfect... Well, it's play. Unless you're an actual cop, I doubt you'll get the cop role perfect, you know? It doesn't matter, though, because it's a game. As long as the two of you are having fun (I'm assuming twos because there was no mention of a third), how accurate it is doesn't matter.
It's all about fun. If you're really really worried, get your partner and yourself aroused before starting. Your brains work a little differently when aroused, and you should feel less self conscious.