Sex life getting boring

I don't feel like I'm good enough when it comes to sex and I want to be different in bed and the way I come across at that moment but I don't know how to do that? I sleep at my fiancés and his mum is sometimes in but goes out weekends and his brother is in then so can't exactly go extreme but all we do is get in bed play down there with each other then have sex but I find it getting boring. Any advice I will be happy with but I will not have any bad comments so type away:)