Based on a comment, natural attacks are not Unarmed strikes, so monk is a bad choice. This leaves ranger, rogue, and barbarian as valid choices.
Natural attacks are not finesse weapons except by dm fiat, so that knocks rogue it off the running.
Than we have 5 levels ranger, druid * to give us 2 attacks + s hours breaker attack.
I could not find anywhere that Mentone I'd hord breaker works with multi-attack, if it dies than only 3 ranger lecture are needed to create a very powerful wild ahape that attacks multiple times per round.
The Rangers 1/2 spell progestin is a nice bit of extra spells, and using unearthed arcana ranger, the potential extra savage against a creature type can be handy.
But barbarians are a smudge superior to Rangers
You get Unarmored defence while in wildshape, ( not sure how the barbarian Unarmored defence interacts with natural armor, one probably supersedes the other) but regardless having 10+ con + dex ac, is better than most other wild shaoe acs.
Level 3 gives resistance to everything but psychic (one of the better choices), and you still get 9th level spells.
Level 5 gives fast movement and an extra attack, extra damage from rage. But all in all it will only give aprox, +5 dpr vs an eventuql 9th level spell slot, and slower wild ahape progression.
To compare the two.
Barbarian 3, druid 2, does
2d6+6, 1d8+6 damage while in bear shape.
Ranger 3, druid 2 does
2d6+4, 1d8+4 damage (if multi-attack triggers hord breaker, an aditional 2d6+4 damage)
Barbarian 5 druid 2 does
2*(2d6+7), can use wild and reckless to get advantage on attacks, and has resistance to pretty much everything.
Ranger 5 druid 2 does
2*(2d6+4) against 1 target abs 2d6+4 against his buddy.
Average damage for L5 characters is
19.5, (+ 11, dms descision) ranger
For L7 characters it is
28 (barbarian) Vs
22 (+11 vs, adjacent enemy, ranger)
Of course the barbarian can opt to stick with 3 levels and go for a faster spell progression.
Ranger works are laughable, not really worth mentioning.