shoes to walk in

http://shop.nordstrom.com/s/mephisto-yael-soft-air-sneaker-women/4676568
or
https://www.shoes.com/mephisto-laser/477190/1600326

You cannot go wrong with Mephisto. And, many are made in Portugal.
https://www.yelp.com/biz/mephisto-portuguesa-fábrica-de-calçado-viana-do-castelo

But, it appears there is no place in Porto to buy them.

Marci - there are many good brands of ladies shoes to choose from: Alegria, Clarks, Merrell, Keen, and TEVA are some of the top brands that come to mind. Find something comfortable and something with a rubber sole that will grip the pavement - no smooth leather soles!

Get them soon, too! So you can know for sure that they'll be comfy.

I've worn Ecco shoes since moving here. Ecco Yucatán style sandals are wonderful. Abeo (Walking Store) are also great. When choosing shoes, not only do they need rubber soles (not smooth), but be sure the soles are thick. I purchased one pair with not as thick soles, and I could feel the cobblestones through the soles of the shoes.

Even with great shoes, be very careful if it happens to rain. The cobblestones become quite slick when wet.

How right you are. I went down on the street in Lisbon and I think that was the only time in all of my travels that I came close to falling on my butt.