The problem with bringing in a kitten is their EXTREME playfullness. If the new kitten doesn't have a playmate, she will no doubt pest the heck out of your current cat, and this could hinder the bonding process. A pair of kittens often in so much better. They have each other while the current cat gets used to the whole idea of them. Just remember to LAVISH attention on your current cat and make introductions fun and rewarding.