Hi ladysmom,
Getting an older dog can be iffy if the dog is not been around cats before. A younger pup will grow up around the cat and although he /she may torment the cat at first , treat it like a playmate, one real swat from the cat can put a pup in its place, where as an adult dog may not be as forgiving. If you adopt a grown dog ask how it gets along with cats beforehand. Introduce them slowly, let the dog get the cats scent in the home for a few days before introduction. Then place a baby gate between them and let them view each other through there, this way the cat will be safe if the dog reacts negatively. Feeding the dog human food such a hot dog pieces or chicken pieces whenever the cat is near can make the dog associate good things happening to him when the cat is around. But only give this if he is behaving. curiosity is okay , but barking and lunging is not a behavior you want to reward him for. Also no matter what you choose, training should be started right away so the dog learns what you will and will not accept.
I am going to direct you to a site of dogs that have been known to be allergy friendly. Just click on a breed and a page will open on that breed. The Bichon is known to have a good personality with children and other pets.
http://www.dogbreedinfo.com/lightshedders.htm
Clicker training
http://www.clickerlessons.com/
video http://www.clickertrainusa.com/clicker-training-videos.htm
dog training consultant
24 years training & behavior,pet first aide, Therapy dog eval., PA Animal Response Team