So I have always considered getting another yorkie puppy of some sort but have always been hesitant because I don't know how Sasha would react. I don't want her to feel replaced all of a sudden since she has been the only dog in our household for 4 years. Me and my parents have been talking about it for a bit and came up with the idea of using a playpen like we did with Sasha while the puppy is still young before we start letting him/her have some open space to run. The only bad thing is I'll feel bad having to block off areas of the house so the puppy doesn't have full run and I don't want Sasha to get confused and upset. What are some past experiences that you all have had with introducing a new puppy to your household with one of your dogs? Could Sasha somewhat "help" the puppy learn the rules and such with potty training?
Any tips and advice would be appreciated. It's not a for sure thing yet, but I have my eye on a puppy

and we all know once they're in our heads, they're hard to leave.