Your feet and back hurt because you don't walk anywhere and are over-reliant on cars. They shouldn't hurt for small distances, our bodies are quite literally built for walking literally all day if need be.

Also, walking doesn't need to be the only alternative. For medium distances, a bike is better in every single way, both health-wise and otherwise. It's fast, cheap, good exercise, you can store it literally anywhere and even bring it onto the trains for the long-distance travels.