What kind of bathing suit should I get?

I want to get a couple of bathing suits, but I don't know what kind are appropriate. My boyfriends family has a boat and we're going to be down there a lot. His sister always wears bikinis but I don't know if I should wear something like that. Do you think that his family will care if i wear a bikini, they're a little conservative. I just started to get a nice bikini body that I want to show off, how can I show it off and not be uncomfortable with his family?