The Additional Info tab that has the Customer Type field is only available in QuickBooks Online Plus. If you're using the Simple Start or Essentials versions, you can use the Notes field if you're currently not using it for your customers.
You can participate in our Feedback site and write a suggestion about placing Customer Type in the version you use. It's one way of making our engineers aware of the things you like to see in QuickBooks Online.
We're just around if you have other questions.