My two cents
Every field likes to say it's totally different from the other ones that existed before. But often they have more in common that what makes them different. Sure in the details there are differences, but overall there are many fields out there which like Service Design, try to create lovely experiences for the people we serve.
So here is a rough list of these very related fields of Service Design:
Customer Experience
Customer Service
Customer Experience Design
Experience Design
Service Innovation
Service Architecture
Service Management
Service Marketing
Employee Experience (or replace employee with "patient", "student" or any other more precise group of people you want to serve).
By knowing that these other names are used for similar approaches this will help you to find even more knowledge. For example instead of googling just for "Service Design Books" you can expand your search by using some of these other terms.
The term Service Design is also translated in other languages. For example in French we call it "Design de Service". Knowing the local translation can help you find more content on this field but in your local language.