WoWInterface - Addon for shapeshifting druids

I play a druid duo with an IRL friend of mine. I"m speccing as primary healer, and he's speccing feral. So, most of the time I'm a caster, and he is bear or cat. however, the reason we decided to do this is flexibility. when i get low on mana, I switch to tank, and he turns caster to nuke and heal. It's a great system, but one of my biggest problems so far, is I have no way to see how far along my mana regen has come.

I'm thinking there should be some way to add an indicator, either by a percentage number, #/#, or a mana bar present while in animal forms, to give you a better indication of when it would be beneficial to switch back to caster form. Has this sort of thing been asked about before? my searching didn't turn up much.