I have a friend in RL who is the epitome of 'curves are sexy'. She probably weighs about 200lbs, but the way she carries herself exudes sexy.
I also posted in ED about my recent experience at a hot springs resort. It was very interesting to see women of all sizes and observe what made a woman 'sexy' or not. I came away with reinforcement that it has much, much less to do with physical size, but everything to do with how a woman carries herself, how open she appears to be, how easily she smiles...