Postpartum Bridesmaid

I am due June 18 and my brother-in-law is getting married July 23. I am a bridesmaid and get to choose my own dress and wear flats/wedges. It should be a very laid back, backyard wedding but I'm a little apprehensive. I don't have any idea what type of dress to get for my postpartum body nor do I know what to expect. I can't back out of this wedding. Just wondering if anyone has any dress advice or general advice!