What store should I get my graduation dress?

-Ok I'm going into 8th grade. I have 2 order the dress really early. The dress has 2 be ALL white. It has to have straps of some sort. I don't know if it should be long or short. I'm very tall. I'm about 5"11. And the dress has to be either silk or cotton. It can't be polyester, rayon, or spandex. I need help.How about this one I found on my favorite store?

http://www.weddingdressesoutlets.com/out鈥?/a>