Re: Bridesmaid while breastfeeding - am I stressing for nothing.
Understandably to be concerned about this. It may or may not go well but if both are important to you than it can be completely workable.
Here are a few things I have seen or have done that helped:
Pump for the duration of the ceremony/wedding and have someone feed the baby a bottle
When being altered, have the seamstress put built in support. Also, a strap that can be tucked in during the pictures and ceremony can be added so the rest of the time you're supported comfortably.
Only wear the dress during pictures and the ceremony. Wear more nursing friendly clothes of the same color the rest of the time.
Have the dress to be altered into a top and bottom. Lift the top to nurse.