I'm playing a forest gnome wizard and as part of my backstory, I've befriended a squirrel, using my Speak with Small Beasts race feature (PHB p. 37), and it follows me around. The squirrel is mostly for fun roleplaying moments, since mechanically it doesn't count as an animal companion or allow me any big benefits. One of my long-term goals is to be able to cast wish to emulate the Druid's awaken spell, thus giving sentience to my best buddy. However, that's still quite a ways off.
In the meantime, I was wondering if there's some way to turn the squirrel into my familiar. From what I understand, the find familiar spell summons some kind of spirit to become my familiar... but I don't want a spirit; I want this one specific squirrel.
Is this possible?