My first suggestion is to research what you want, a therapy dog is not a service dog as stated. A therapy dog is a dog trained to do such things as visit sick in hospitals, nursing homes or schools, where they go and listen to children read stories or work in class rooms as a classroom pet for children with disabilities or behavior needs.
Once you research you will find service dog is more likely what you want. Then you must determine what services your son needs a dog for. I have heard of service dogs for autism, usually for young children, they will help with things like not allowing the child to bolt into the street, or to calm a child by placing there weight on top of them.
You also need to research a lot, because my understanding is all dogs for autistic children are tethered to the parent, and it is the parent who makes all the commands, I could be wrong about it being all, but that is my understanding, so please research and ask lots of questions since your fear of dogs may play a big part in if a dog is right for your family.
If neither a service dog or therapy dog is what you want than you may choose a dog that can help with just calming your son in the home. These may not have to be a service dog, they are usually called a companion dog. They can play a huge roll in calming a child just by having a dog. A lab is a great family dog and usually bonds the best with the person In The home that needs him most. It can effect the child's moods, help in calming and also play a huge part in socialization and language skills, mainly because a cute dog will bring friends over to your child and he will have friends who want to learn more about him and his dog. These dogs do not necessarily have to be service dogs, a good trainer can help train a dog for this purpose for far less than a service dog would cost. If you choose to go this way, call your local human society and ask for a trainer in the area and talk to who they recommend. This may cost you $500 to a $1000 for the training compared to $10000 or more for a service dog. It depends on if you will always be with your son and need the dog to service your son outside the home, or if it will mainly be a dog that you have just for home, which most schools find children to young to handle a dog and most public schools will not allow dogs until age 16, because even with ADA, you have to weigh the benefit for the child compared to the benefit of all students and again an autistic service dog is usually handled by the parent and not the child so would not be allowed in school.
I hope this helps, I think you are confusing people and getting some off answers because you are linking service and therapy dogs as one, which they are not, but I think what you really may want to serve your needs is a companion dog, which is totally different than a service or a therapy dog. They also have different rights, service dogs come under ADA, companion dogs come under HUD as approved in housing and have the same rights in housing only as service dogs. And therapy dogs have rights that are totally different and never do a service for any one individual but a service for a group of people with the same common link, such as all students who need to learn to read, or all elders in a nursing home.
