If you're interested in old cast iron mostly because of the smoothness, look hard into carbon steel. You use the same seasoning methods, but it's smooth from the very start and somewhat lighter while still having great heat retention.

One caveat - of you're using induction heating you want to be sure you get thicker carbon steel at 3mm - some 2mm pans will apparently warp a bit and can become "spinners" with a not quite flat bottom surface.