I have been measured for a bra at different shops and been told different sizes. I was also told that different styles may mean you need a different size. I measured myself once and got a different size to the other two. I was told by a friend that you really need to go to a corsitier for a correct fit. I have been measured over tops, bras and no bra on. I have also got bras in exactly the same style and size from the same shop and they have fitted differently. I despair.
It's a total nightmare. The best, undoubtedly are Rigby and Peller - corsetiers to HM The Queen. Unfortunately the bras are quite pricey and for some of the brands they sell they are the sole UK retailer. After R&P, I would rate John Lewis, and also Bravissimo. I had a very poor experience at Marks and Spencer (where the fitter didn't seem to understand how to convert the measurements in to the right bra size. I've not had fittings anywhere else, so cannot say if any of the other stores are as good or better than R&P, JLP and B.
Once you find a style that suits you and you've got the correct back and cup size, it's good to look for similar styles from the same brand. One thing to remember is that if you are buying black bras (black any item of clothing) it is always stiffer and less stretchy than other colours - something to do with the way the dye affects the fabric.
A good fitter will be able to explain what to look for, which then makes it far easier for you to find your own good fit on future bra shopping visits.
The technicalities of bra fitting means that in general you're never going to get QVC retailing what you need. The best you can hope for is the shapewear tops and the Rhonda Shear Ahh Bra. Ironic, really, when the foundation garments are really what make the clothes look their best. Let's face it a lot of the nonsense we see when shapewear magically improves the appearance of trousers, tops and dresses is down to the purposeful and cynical use of badly fitting underwear for the before shots (as well as the models' posture changing between the before and after shots in some cases).
I think clothing sizing everywhere is enough to drive anyone demented... they keep resizing everything to keep up with the average body. We get bigger every year but think we are staying the same because we can still get into whatever size is our go-to... but if you compare a 12 of 20 years ago with a 12 now it is probably nearer to a 14 from 20 years ago.
I would hesitate to call today's sizing vanity sizing, as some of the dimensions of yesteryear could be attributed to some quite brutal non-stretch shapewear which is no longer in vogue. But I would say we're all lulled into a false sense of how well we are maintaining our shape and weight by the dress size we wear.
All clothing is made with a "tolerance" which is the amount either side of the standard dimensions for a size (plus or minus) which is permitted. So it is always worth picking up more than one of the same size in a garment to try on.
Clothing cut for a young girl in the same size will probably not look at all flattering on a woman who has had children but is the same dress size. So it's worth bearing in mind the target customer for a shop.
I've always found that Wallis have forgiving sizes for me, whereas Next don't. It's some of it down to the individual styles - some leaner styles are not going to give you the wriggle room and are better sized up.
This is not just a problem for larger sizes (though the laziness of not using fit models and having bizarre progressions from one size to the next doesn't help). Look at Jill Franks - QVC fashion does her no service whatsoever. She's been on air with bulldog clips down her back so she doesn't look too swamped in items. Sometimes the slimmer models are too slim (yes, Deborah-Ann, I mean you) to look good in the items they wear too.