Who wants a buddy?

[Lychee]

I would, as soon as I can eat the berries and recover (do I have to do just that in one action?)

Buying/Eating berries is a free action
Hiring a merc is probably also a free action!
So, you should still be able to take a full action on your turn, once Lillian hires a guard for you.

Which pokemon species do you want as a buddy?
It is a good idea to pick one that covers your type weakness somehow, and also think about their relative speed/size/hit dice used in battle.