E.W.
I know exactly what you are talking about I am a 38DD and I have the same problem. I used to buy all of my bras at Victoria Secrets but then they started making bra's that just were not for me. They are more geared to a smaller bust size. I did finally return to VS a few months ago and found a bra that I love (the body by Victoria, full coverage, under wire bra). It is very comfortable, separates, and I do not fall our of it (like you mentioned). It does not give me as much lift as I would like, but it is enough to not sag. I really love this bra, and I am very picky about bras! I would also recommend Frederick's of Hollywood. I have not bought a bra there in a while, but last I remember they sell wonderful bras! They last a LONG time, and give you lots of lift. I just wore out one of the bras from Frederick's that I have had for at least 6 years. Good luck shopping, I know it can be frustrating.