For bras, you can measure yourself - follow this method:
thebetterbracampaign.blogspot.co.uk/p/fitting-advice.html
If you post your measurements, then the MN bra gurus will help you! Or you can work it out yourself if you prefer.
You need to measure under your bust, pulling the tape quite firmly - that is the bra band measurement (none of this "add 4 inches" nonsense that M&S etc still do). If you're between sizes, then probably size down. Then measure around your boobs while leaning forward. This sounds really scary (or did to me at least!) but go with it! Then for every inch that measures more than your underbust measurement, go up a cup size - it starts at an A cup for 1" more and goes: A,B,C,D,DD,E,F,FF,G,GG,H,HH,J,JJ,K,KK,L... The bra size you get will then be your starting point to trying a load of new bras. If you're D cup or above, Bravissimo may be your best bet. You may need to try a few different styles and a few sizes around your starting point to get your perfect bra.
It sounds like a massive hassle, but seriously, it is so worth it - it makes such a difference to how you feel and look.