Okay - regarding mixes. I had decided about 2 years ago that I wanted to adopt or rescue a Yorkie. It ended up taking about a year for me to find the dog that was best for my family. It took a lot of persistance, but it did finally happen and we ended up with our wonderful Sandy who is around 7-9 years old (a cairn-yorkie mix). I could have just bought a mix, but as you said they are expensive, around what I was willing to pay for a purebred Yorkie, and I couldn't see paying that kind of money when there were dogs out there who needed good homes (this is ME, I have no problem with other people doing this)
I wrote a little something on my page about rescues and olders dogs:
http://aimeecentral.com/doggies/whyrescue.html http://aimeecentral.com/doggies/older.html
As far as bringing a puppy home to an older dog, Sandy ended up doing SO WELL when we brought Tia home. Since day one she's been like a Mommy/Sister mix to her. The only thing we had to make sure of was to give Sandy a lot of extra love and attention, and that seemed to ease the transition for her
I hope this helps you a little
