How about reskinning the barbarian as an animal?
You might use the ability scores/abilities for a human variant totem barbarian, but you are a giant wolf, panther, etc... Perhaps one that was awakened?
I did this. In the module B10 one of the random encounters is an old guy giving the PCs a 2HD war dog. I had already had an inkling the dwarf paladin was going to quit the party so adding another frontline PC was helpful.
Since it was a dog it was, of course, a wolf barbarian (3rd level to begin with). It isn't much offensively as its bite is only 1d6+STR but I did allow it to be trained and get the ability to knock down opponents as a bonus action. The advantage to allies is nice and makes up for weak offense. Since it's a dog NPC it's really easy to roleplay. Also, none (or almost none) of a barbarian's abilities are things a dog can't do. The dog only gets 1/2 XP so it's more of a companion. And when anyone drops to zero hp in combat, which happens with regularity, that player runs the dog.