A too small cup can make a bra in the correct band feel tight, which makes people think they need to size up in band rather than cup. This may be your case here. It is worth it to find a store that sells 32DD and try on all the ones you see. And since that is a matrix size, you can even find it in more stores than common "true" sizes like 32F.
A couple examples, Marks and Spencer's bands, in general, run small, so you should try 34D and 34DD from them, in addition to 32DD and 32E. Debenhams has their own DD+ line in addition to selling other bra brands, so you can try on a range of sizes at their stores. Bravissimo also sells 32DD, and their fitters are (typically) in a level above the rest so if you're comfortable you can have one of them help.