That's what I need!
I found something which I thought would work; it's two weird silicon things which stick to your boobs and then you can do it up in the middle to encourage cleavage, iyswim.
It might have worked but I found that being a c cup in a bra wasnt' the same as a c cup in this, and the thing just hung on my breast pointing at the floor and was too small.
I need a bra without straps, or with invisible (or nearly invisible) straps, which will stop my breasts pointing at the floor, and also ensure that they don't flatten out when I'm wearing a top like this. (Not that I want that particular one, but I've been given a couple which are gathered like that and I'm completely flattened by them!)
Please help me! I want to keep my boobs this summer.