You could also try layering sports bras.
You put one on backwards first and then the next one on normally.
You might be able to exercise in it but I would double check that.
DID YOU KNOW: YOU CAN USE A PAD LESS SPORTS BRA AS A CHEST BINDER? WITH MY USUAL BRA; WITH SPORTS BRA; HERE'S A COMPARISON! IT'S A SMALL DIFFERENCE, BUT IT WORKS WELL! I'D SAY A ONE OR TWO SIZE SMALLER THAN YOUR USUAL SIZE WOULD DO THE TRICK! ALTHOUGH IT CAN BE PRETTY TIGHT.. BUT ACTUALL CHEST BINDERS ARE ALSO PRETTY TIGHT. HU; THE ONE I USED IN THE PICTURE! ⏬