My bra doesn't sit on the middle part of the breasts.?

It sounds like your band is too large and/or your cups are too small. Your band size should be roughly the measurement around your chest, under your band. Band sizes go down to 28, so don't feel that 32 is the smallest they go. When you go down a band size, you have to go up a cup size to keep the same cup volume, so if you try a 30, you'd have to try a 30DD to keep the same cup volume of the 32D that you are currently wearing. If you find the bra feels tight when you go down a band size or two, first try getting a larger cup because that can make the band feel too tight, also.