I'm not sure if you could raise your animal companion level past your Druid level, but you could always be a Pack Lord Druid and take Boon Companion twice to buff the level of each companion, and have two max level companions until level 9.
If you are an Aasimar, you could take the feat Celestial Servant to give your animal companions the celestial template.
I don't think as it stands there is a way to do this via Druid, but a Lunar Oracle should fit what you're looking for just dandy. Just take the primal companion revelation:
Primal Companion (Ex): You gain the service of a faithful animal of the night. You can select from a bear, boar, crocodile, shark, tiger, or wolf. This animal functions as a druid's animal companion, using your oracle level as your effective druid level.
After that, use the favored class bonus of an Aasimar Oracle:
Oracle Add +1/6 to the oracle's level for the purpose of determining the effects of one revelation.
The original version of this (before a July 2015 errata) let you have +1/2 instead of +1/6. Despite that, you can use the spells Righteous Might and Divine Power (which stack and can be cast on your animal companion via the Share Spells feature). Also look into Divine Vessel for a disgusting display of animal companion power.