Ladies - bra help!?!?

Been, there done it.........I have bought from the most expensive to the cheaptest of 'bras and have came to the conclusion you only get a good fit by 'trial and error' and usually you are unlucky 9 times out of 10. M & S, House of Fraser, Bravissimo, Debenhams....Need I go on? Have all measured me and came up with different sizes. I am probably a lot older than you so believe me try on, look at it, if you think it might fit you try it on and only then will you know if it's a good fit.