It does not matter if you are big or small, if you slouch in your chair, it doesn't look good. If you stand tall, you look confident. If you believe what I'm saying is true, that you are a worthy person deserving of confidence, and you go through your days conciously displaying confidence, people will treat you as a confident, worthy person and eventually, you'll become more confident because of it. Cultivating the feeling of being sexy is very similar to getting the feeling of confidence. The two really do go hand in hand.
Confident women do appear sexier.
Notice how other women behave in social situations. Much of the behavior you will see is a result of being confident in themselves. Let laughter come naturally, a woman gets a certain kind of light in her eyes, and flush in her cheeks when she laughs, and that can be very attractive. Of course, only laugh when its actually funny, a forced laugh has the opposite effect. Never or rarely laughing makes people think you don't have a sense of humor, and you aren't able to really have fun.