Interesting about the dense thing. Not only have mine not got bigger since being pregnant, but they've sort of gone south - I turned 40 at 4 weeks pregnant, so it could be just an age thing (my friend said 'ah yeah, overnight between 39 and 40 my boobs and my bingo wings went south, there was no recovering of them!')
I investigated sleep bras in Mothercare yesterday - not the right size for me, but I'm thinking about those for the first week when I probably won't be out partying all that much - not too concerned about breast shape under clothes!