I always think its great to have a companion character in games so I reckon you're going down the right path.
A cool idea I had would be you could temporarily tame the monsters with a bit of food so that they don't attack you for a while, but if you leave it long enough they then become aggressive again. Maybe from that if you feed them enough you could befriend them and they evolve from their regular form into a companion with their own health bar for you to protect.
If the companion takes to I many hits and dies maybe it could spawn something like a revival item. Then after a certain amount of carriages you could revive them at an altar of sorts.
That's one idea that I think wouldn't be bad to have in the game.