I agree with Trish, a neutered male will do best with your spayed female. Two females can be trickier and will depend a lot on their personalities...it can work but the safer bet is a male kitten. And DO quarantine, so many give in and let the kitten out and live to regret it as mentioned above. Add to that any health guarantee you have on a kitten is void if you don't... but as one of the directors of Savannah Rescue I can tell you that a lot of angst and difficulties can be avoided if you just do the quarantine and introduce slowly...better to have that minor inconvenience at first than a major hassle later on when they really don't get along and you have to backtrack and work harder and longer to make it work!