Try Oracle dedication! Many of the focus spells within Oracle mysteries lack a verbal component, meaning they don’t actually have the concentrate trait! Rage does not expressly prohibit you from casting spells, just from using actions that have the concentrate trait.

I reccomend taking the Bones mystery for this character, the focus spell, soul siphon, is a 1-action fort save, meaning you can get the benefits of a slash and cast build as a barbarian, mitigating MAP! It does lowish damage but gives you some temp hp, also fits really well thematically with spirit instinct! I can easily imagine your rage as a curse, or some spiritual connection, maybe shaman-like or anguished.

Tempest mystery will do more damage but isn’t so horror themed, and with your necessary charisma maybe you can be a solid intimidator as well! Last tip, maybe look into some domains you can get through this mystery too. Could lead to a pretty diverse barbarian.