So... kind of a weird take on my end: Warlock familiars should be expendable.
Extremely expendable.
Like. You should plan for them to die and use their death to your advantage.
So I'd recommend an Invocation that allows you to get your familiar back for free at the end of a short rest! No minimum level. Also causes your familiar to leave a body behind that you can pick up and mourn over, or leave on the lonely cobblestones, as appropriate.
And then a later invocation that allows you to resummon your familiar, regardless of where they are or if they're dead, as an action, after level 5 if you have the short rest invocation.
Then you can send your familiar out onto the battlefield to act as an extension of your will, watch it get schmucked into the dirt, and cast
Corpse Explosion on the remains...
Then resummon it the next turn and see if your enemy is foolish enough to kill it, again!
... gonna go ahead and add these options to my Occult Omens materials...