Morning both, I'm no expert on BF bras etc so hopefully StatiscallyChallenged or HazelNutt will be along to help soon!
However, I will just ask you both if you're sure you're wearing the right size (bra bore alert).
OK, here goes. Measure under your bust (hold the tape tight) to get your band measurement. Then measure across the fullest part of your bust. Each 1" of difference between the two measurements equals a cup size.
So, Mama, let's say you measure 30" underneath and 35" across? That would give you a starting point of 30DD.
The best way I've found to test the band size is to put the bra (in your case a 30 back) on back to front. If you can breathe but if feels tight and you can only fit two fingers underneath the wire at the front, then that's the correct back size for you. If it's so tight it's unbearable then go up a size.
Once you've got the back sorted, it's time to get the cup right. The cup will differ much more between brands and styles than the back (IMHO). Turn the bra round the correct way, lean forward and using your hands, scoop all your breast tissue into the cups (make sure you get all the flesh from round your back and under your arms in). The put the shoulder straps up and adjust as necessary (not too tight as it's the back that should be doing most of the supporting work). If for example, you've started with a 30DD, you will probably find that after scooping, you have some bulging over the cup and quadraboob going on! This means you need to go up one or more cup sizes. Keep going up through the cup sizes until all your breast tissue is firmly in place.
disparate Are you absolutely sure you're a 36? Droopiness is very often caused by wearing too big a band.
Good online shops are Bra Stop, Figleaves and Bravissimo. If you order online, then I would try three styles (full, balcony and plunge) in a few sizes each so you can get a really good idea of what fits and suits you. Boobs that are fuller at the top usually suit plunge and those that are fuller at the bottom (like mine) usually suit balcony. Avoid M&S like the plague. They can't fit for toffee and the bras are poor quality. John Lewis and Debenhams stock good ranges though but beware of any fitters that measure you and try and add the dreaded 4 or 5 inches!