I know what you mean. Heck, if we hadn't gotten Toto first we probably would never have had Sassy: she came from the same pet shop we got him from; her previous owners had returned her. Mom went in to get something, saw Sassy and the shop owner said if Mom wasn't interested then she'd probably become a store cat. Mom brought her home, we fell in love with her, and that was that.

Sassy probably wouldn't mind this being a one-cat home, or even just a one-pet (her) home. That's the other thing we have to consider - any new animal we bring in will probably put her nose way out of joint.