What is the best breed for a service dog in my case?

Have you got a local service dog charity to speak to? You may find the best "breed" is actually a mongrel! A lot of non-seeing eye dogs originate from rescue centres, so you will see a lot of mongrels as successful service dogs. A large Golden Retriever, German Shepherd or even Standard Poodle cross could probably do the job, it all depends on what the local service dog trainers have access to!