My Yorkie is 7 lbs and to me he is tiny! We have always had big dogs and even growing up my small dog was a fox terrier who weighs twice what my Yorkie weighs. If yours is too small to get on the couch easily make little stairs at one end of the couch for them to climb up to get on/off the couch easier. My Yorkie jumps on the small couch at the foot of my bed and then from there jumps onto the bed to make it easier. In the morning he just waits for me to lift him off the bed and carry him upstairs with me.
I think a 4 or 5 lb Yorkie would be super cute, but my 7 lb guy is pretty awesome just as he is. I carry him around all over with me and he really doesn't get heavy for me so I guess him and I are just perfect for each other.
Today I was holding him and just looked at him and said "where have you been all my life?" He just snuggled against me, I think he was thinking the same thing I was.
Good luck with your little one. I hope they end up the perfect size for you
