Someone upthread wanted to vote hetty in for PM - I'd like to second that!
I am another correct-bra-fitting ambassador and often find myself wanting to go up to strangers and point out the error of their ways, yet my knowledge pales into insignificance when it comes to hetty's!
To add my twopence worth, here are some of my tips:
For you ladies struggling with the tight band thing - it does get better as you get used to it and it's never as uncomfortable as a pair of poor fitting shoes and makes you look 100 times better. Also, for those of you slightly aghast at spending more on a bra than you might normally, think about the cost per wear - it comes down to almost nothing and it's an investment, not a cost, particularly when it makes you look and feel great. Get shopping!
I also find that some makes absolutely don't work for me e.g. Berlei, whereas Freya (available John Lewis, House of Fraser and Bravissimo) is brilliant, but that's for me. Even then when you think you have found a correct fitting style, sometimes the fabrics make a difference to the fit so even if you're say a 32F one time, don't be surprised if you need a 34E or even a 32FF in apparently exactly the same style the next time, if it's a different fabric e.g. stretchy soft cotton vs nylon.
Don't be afraid to take in loads of different ones into the fitting rooms, both styles and sizes within one or two differences. Oh, and colours too - even if you hate the colour and the fit is good, you can probably order a preferred colour on-line somewhere - at least you'll have the correct size and style.
Back fat can be an issue but it's one that looks far better in a well fitted bra than a poorly fitted one.
Hope this helps and for those of you who are discovering the joys of proper bra-fitting - hurrah!