You could just set the key of the song in major key (C instead of Am). That would solve the problem.
If you set the key to A minor, than logically the Am chord should be the number "1" chord (first degree of the minor scale).
You probably know that there are three minor modes (dorian, phrygian & aolian). What you suggested would only work for aolian minor modes (the relative of the major mode). Some songs can also be in dorian modes or phrygian modes. This is why it's better to consider the first chord of a minor scale as the number "1" (the "home" chord where it always resolves)