I had a formal wedding in December and wore a maxi dress from Jeans West - just singlet straps that I was able to pull down and feed in. The venue didn't have a feeding room as such but they had a foyer area with comfy couches that I sat on while everyone else was seated in the main room. Most reception places have a lounge/reception area so that might be an option too and if you use a pashmina shawl to stay warm, it can double as a cover while you feed so even if you wear the dress you have, you can get someone to help you! I think I got DH to unzip me prior and then he helped me get dressed again! Enjoy getting all glammed up! I loved it!