I'm a 36D and have a lot of trouble too. I've been looking for the past couple of months now!
And why on earth do so many manufactures think bigger breasted women want elastic straps!

Also when I try on a bra that has a padded strap that is supposed to be at the top of my shoulder it ends up at my collar bone!

I have always liked being bigger busted but NEVER liked having to wear uncomfortable bras or bras that stretch out and lower my boobs by an inch!
I'm guessing that being saggy and baggy has something to do about it! sigh