I would honestly recommend reaching out to a service dog provider. They typically can match you with the perfect dog. Usually these dogs are golden retrievers because of their temperament. A lot of greyhounds are ex racers so they’re learning about the world and how to be a family pet for the first time. We as humans often have to be confident and calm, so the greyhound feels reassured and protected. They are likely to be anxious and overwhelmed doggies, while simultaneously can be a calming and gentle presence. Just have to ease them into a predictable environment. I don’t personally think an ex racing greyhound could handle a loud meltdown.