To be considered a service dog in the USA, a dog has to be trained to do something specific to mitigate your disability (so there has to be a disability).

It sounds like maybe you would be more interested in an emotional support animal. They are animals who help with reassurance and confidence simply by being present. They require far less training. However, a person with an ESA does not have the same access rights as a person with a service dog. Many places will allow you to have your ESA with you even though they don't have to. Because they don't require the same kind of training as a service dog, they are far cheaper to either purchase or train yourself.