A Ring cheekpiece introduces poll pressure as well creating leverage on the mouthpiece, the 2½ Ring version is the softest version of ring bit as the ½ ring softens the leverage on the mouthpiece and poll.
The Happy Tongue is a solid mouth piece. It is curved and ported to give tongue relief. The Happy Tongue would be a good place to start if your horse is:
The rider will know immediately if this is the correct bit, as a horse with a sensitive tongue will finally begin to work into, and accept the contact. Changing the cheekpieces would then allow the rider to adjust the level of control.