As someone who owns a bridal shop, let me say that discrimination against the voluptuous woman does happen, but it doesn't happen everywhere. (I do hear horror stories all the time.) I would honestly call shops before you go and ask frankly what sizes they carry and explain what you're looking for and what your budget is. Many shops specialize in plus sizes - it's a (pardon the pun) growing need.
Also, I have found that, for bridesmaids, often the other members of the bridal party can be quite rude to the larger women. After measurements are taken I like to privately discuss with each person where they fall on the size chart. Leave it to the skinny little sisters to pester to find out what size the heavier girls ended up ordering. My reply is, "none of your business what size anyone orders."