Help me find a dress?

I need a dress for something in school. Its supposed to be a casual/semi formal dress. Im about 5.2 if that helps. Im slim and have a 'dancers body' but with arm muscle. Id like a navy or white one, but any colour's okay. Id like it to go just above or below my knees since it has to be okay to wear in school. Oh and for the fabric id like one that they make dress shirts out of? like twill kinda. or cotton. Nvm anything would be good. Help me find one?