They are expensive, but Enell are meant to be the 'Rolls Royce' of sports bras. Figleaves.com sell them, but they aren't listed if you search by brand, only if you search for Enell. The sizing is a bit odd (I'm a 32E and would have to get a size 0) but it is explained on the site. I haven't had any experience of them but have heard that bouncing is a thing of the past with these.

Sorry to those who like M&S but they have always got my sizing wrong when they have measured me - band size two sizes too big, cup size four sizes too small. Go somewhere like John Lewis, House of Fraser, or best of all Rigby and Peller. Once you know your size, then by and large you can shop almost anywhere... just adapting to suit different brands.