Think of the Moon Druid's shapechange as "unlimited, but you have to take a break and recharge for an hour every once in a while."
Seriously, 2 shape changes per short rest is fantastic.
Would having to trade spells slots for an extra wildshape balance it? Such as if you want an extra wild shape you have to give up 3 1st level spell slots. Would allow moon druid to shift from primary spellcaster to a front line fighter without being able to cast spells all day long after their wild shape is over. Also a nice way to scale it with levels

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.