Gastric byp fitting in my dress?

Has anyone had gastric byp surgery? I need some advice. I am getting gastric byp surgery in September/October of this year, and I am getting married next August. How can i have my wedding dress be sure to fit me if between my surgery and then i'll be loosing lots of weight? Is there any estimate i can determine i'll be by then? Right now i am 280 lbs and 5'6" I wear a size 22 dress. I'm nervous about ordering a dress if its gonna be way to big by the time my wedding comes around. I know they can make alterations but there are limites on how small they can make things- especially depending on the dress style. Any suggestions or ideas on how i can make things work out i'd really appreciate it!