List of Generic ScriptableObjects? Wrappers maybe?

So I have an class, Thing, which is a ScriptableObject.

I want to keep a list of Things, but Unity won't let me without actually implementing a type for T. So I could only do a list of, say, Thing, Thing, but not a list that contains both Thing and Thing.

What I want to do is keep track of these Things in one list, but be able to access specific Things or whatever in the list.

I understand a little about interfaces, and I have heard of wrappers, but I'm not exactly sure how this sort of thing works. How can I create a List that can contain references to multiple types of Thing?