I have the same issues. I love my Lane Bryant plunge bras (never heard I shouldn't wear plunge & love the cleavage they create) & am currently looking for a replacement since I need a smaller band size than they carry. I do know that after the LB plunge, I have always needed demi style bras because of the lack of fullness at the top of my breasts. I checked your size with this calculator: http://www.sophisticatedpair.com/bracalculator.htm
& it says you should be wearing a 32I (with snug band), 34H (moderately snug band), or 36G (slightly snug band). I like that calculator because it is the only one that I found that matched the professional fitting I had a couple of months ago. Now I feel like I can trust it as I lose more weight & need new sizes.