I'm a little glad you didn't do the names idea because I can't spell for the life of me so I would have failed. Not including the 1's and 2's might have been fine though, especially 1 because it just meant I could fully ignore multiplication and division. With that I could also just not put in any animals to substitute as 0 and also ignore any unwanted subtraction and addition.
As for animal names if you want a 2 letter English name might I recommend the Ox. Want to keep a 1 letter animal you can stretch it a little and just add a B :) who needs the 'ee' anyway