Singular and Plural

I was thinking of starting up a small zoo, so I wrote a letter to London Zoo,
"Dear Sir, I'm starting up a zoo, please send me 2 mongooses"
I thought that didn't sound right so I tried again,
"Dear Sir, I'm starting up a small zoo, please send me 2 mongeese"
Nope, that still didn't sound right,
"Dear Sir, Im starting up a small zoo, please send me 2 mongi"
Ahh fuck it I thought,
"Dear Sir, Im starting up a small zoo, please send me a mongoose".
" P.S. Send me another one"