I worked as a bra fitting specialist and an Australian store and I too cannot find a comfortable bra despite being surrounded by them. But that's mostly because my size changes between meals lol.
Usually the bra riding up at the back means that the back size is wrong. Most women wear the wrong bra size so even if it's embarrassing I suggest everyone get fitted by somebody who knows what they are doing and also know the best bras they carry. We have this one bra that almost every woman with a larger bust walks out loving, has generous straps without being overbearing and good support.
But saying this, I'm a hypocrit because I never buy the ones I should, and I've never been fitted haha. Hate bras!