American Dance Supplies' Posture Reminder is exactly that. No more slouching... it reminds you to not slouch.
Size XS-S (30" X 1.5"), S-M (35" X 1.5"), M-L (40" X 1.5")
Size XS-S (30" X 1.5"), S-M (35" X 1.5"), M-L (40" X 1.5")