I want to get another cat but I am afraid I will upset the other two (who I bough together, brother and sister) and also I am not sure how to go about introducing them...
Only you know your cats so if you are unsure I would recommend you to wait and think about it. It might help doing what I do with the screendoor, then they can get to know the new familymember in their own time without uneccesary fights :)