How hard is it to add to your family of pets?

I want to have another dog or maybe a cat but I can't afford one right now for two reasons. One, since I don't have a stable income right now I can only raise one dog. Secondly, I'm taking care of my aunt's dog, Sandy, too and she's a little diva so another dog will be bullied by her. Perhaps when I finally have a stable job and my own house, I can get as many pets as I can handle. Right now, I need to attend to these two that I have for the meantime.