*Information adapted from Best Friends Animal Society*
Choosing a new cat
The first step is to pick the best possible new cat for your household and lifestyle. A cat that have lived with another cat are more likely to get along with other cats than one that hasn't.
If your cat likes to play, getting another playful cat is probably a good idea. If your cat prefers to relax, you're probably better off adopting a cat with similar habits. A kitten or young cat is probably not a good idea for a household with an older or grumpy cat.
Bringing in a new cat
Before bringing your new cat home, create a separate space for them with food, water, a scratching post, a litter box, access to natural light and comfortable resting places.
Place the new cat in their space as soon as they get home, and spend at least one hour per day with them. Play with them and watch for any signs of stress or anxiety, such as hiding, aggression, decreased appetite or excessive vocalization. If any of these signs persist for more than several days or if the cat stops eating, consult your veterinarian.
Cats have glands in their cheeks that produce pheromones, so try gently rubbing a towel on each cat's cheeks and exposing the other cat to the towel. This will help each cat get used to the other's scent.
Next, place the cats on either side of a closed door so they can smell each other. They can then meet through a baby gate or a door that's propped open a couple of inches. If they seem interested and comfortable, allow them to meet under your supervision.
If either cat shows signs of mild stress, give them time to adjust. If both cats seem comfortable in their spaces, place the new cat in a different room after a couple of days and allow your other cat to enter this new territory. Each cat should have their own space with multiple hiding places if needed. Large cardboard boxes with holes cut in two sides can work as hiding places. The second hole allows the cat to escape if cornered by the other cat.
If either cat shows signs of severe stress or aggression, separate the two and introduce them more slowly. Once they gotten comfortable with smelling each other through a door, place them on opposite ends of a large room. Place the more comfortable cat in a carrier with food and play with the other cat. Gradually bring the two cats closer to each other over several sessions.