No mixbreds are not healthier than purebreds and in fact can inherit health issues from both sides of their family tree.
What I would suggest is looking for a middle age or young senior dog to adopt that is in the size range and has if possible a known health history.
I think in Florida you have a good chance of finding just what you want available to adopt.
With an adult dog you will have a good idea of just what the dog's energy level and personality will be when you meet them which is harder to predict in a pup and of course all pups are pretty busy anyhow.
You may want to take a look at http://www.petfinder.com/ and put in Dog, Small, Adult and your zip code to see what dogs might be available for adoption in your area.
You might like another Yorkie or Yorkie mix or a Pekingese or Chihuahua mix (long coats tend to be calmer), a Maltese, Shih Tzu or even a Poodle mix if you can handle grooming.
But you may find a who knows what type of mix with the perfect temperament for your home if you search a while.
You may want to contact some of the rescues in your area that work with small dogs and see if they have something for you - petfinder is a good place to check them out.
I saw in Central Fl for example Li'l Lap Dog Rescue http://www.petfinder.com/shelters/FL515.html
that might have a dog and you can always check and see if more distant shelters have means to help transport a dog to the right home.
Hope this helps you!
Dog Expert:Rescue, Train,Breed,Care
30+ yrs dog home vet care & nursing, rescue, behavior&training, responsible show breeding, genetics