what alternator do i need?

If you have a stocker, no big electric fans, no electric pump, no huge stereo, etc,

literally millions of cars were on the road for years and years with a 30-35 A alternator.

Yes, the lights "dim a little" at slow idle. I'm not sure when this got to be a big deal. When I was young, that was the way it was, and things worked fine.