I received my first binder yesterday - let's say there's room for improvement [emoji13]. I ordered from a European company. The first one was too big, so I returned it. The new one is now size XS/S (it's a strapless one with a bra clasp) but it still doesn't do the job properly.
Anyway, it's probably good enough to get used to the thing and creating a bit more ambiguity. I'll probably try to find another solution though...