Another thought for those looking, is a material that won't wrinkle a lot. Low maintenance is a wonderful asset in a white dress. I don't know how many times I'd throw off my dress before running to breakfast, put it in a bag and forget to hang it up right away. Never needing to iron it was wonderful.
Also, something that is easy to get in and out of. If you are unwilling to walk outside in your dress (aka january in Wisconsin) and you need to change in the house, don't count on the luxury of having the bathroom to change in, usually it was the living room.
the joys of an overcrowded house, ahh but the wonderful memories.