The historic cities in Minas Gerais are certainly an alternative. They are called "historic" because they boomed in the 18th century when Gold was found and heavily mined there. These are smallish cities with a heavy Portuguese influence that tend to be very pleasant. Tiradentes has become somewhat fashionable.

If you are looking for nature I think Iguaçu may be an alternative, about 600mi/1000km from Sao Paulo but depending where you are in the countryside of the state it may be considerably closer.

Finally, I see that Rio is not in your plans but I would suggest having a look even if just for recon.