To best support the expectations of the platform and any business logic, attributes, etc. as well as the future growth of your company's service management program you would be well advised to use the CSDM CIs and relationships. I would simply create a single default Offering for your Service.
I would look at it like this: it's not that you have no offering. You have only one offering. It's not necessary that you have defined service commitments in order to consider it an offering. The service represents the value that is delivered to consumers, and the offering represents how that value is delivered. If you define a service without an offering, that's having the what without the how. That won't serve you well.
The opinions expressed here are the opinions of the author, and are not endorsed by ServiceNow or any other employer, company, or entity.
