So I'm a big believer in using 1, 2, 3b, 4, 5, 6b, 7b to think about minor keys.
There's a small complication here, because there are three different minor scales. The one you're using here is the Natural Minor, which is the scale that uses the same notes as a major scale three half-step above it, so Am has the same notes as C.
I think that it is good to be aware of that, but not yet to worry too much about it. (Wikipedia has a page
here).