To add to what SilverFang suggested, maybe a tight bra with a binder on over that, and then a loose t-shirt. You'll be hot, though, with any kind of binder.
You can also wear the Cotton Concealer doubled over. It goes down to your waist, but you can fold it up. If the binder is snug enough, you get a bit of extra flattening power.
It might tend to roll up if you're too active, whether you wear it full length or not. Some guys use safety pins and all of that. You'll have to experiment a bit.
P.S. 34B doesn't sound too bad, except you're verging on a C...and it all depends on your frame, too. And the consistency. I know a lot of guys who were, let's say, droopy; my tissue was always very dense and hard to hide, even when I reached my forties. It sucked.