If there was a magic solution to preventing plantar fasciitis, then no one would have it anymore! Different things work for different people. It's important to find out what works for you. This can be done with experimentation or the help of a specialist.
One thing I would caution against is just throwing more padding at it! There is something wrong with your stride and the padding may hide it for while, but it will eventually come back. I say pay particular attention to how you're walking while wearing your walking shoes that do not give you any problems. Then walk around in your sandals or your boots. Pay attention to how your feet land in the different footwear, and how you transition to your next stride.
Find the stride that works best for you and practice it. I know it's strange to have to think about walking again, it's supposed to be something we just do, but I find it helps me.
When I'm hiking with my thin soled trail running shoes, I have a tendency to step and land on the front of my foot and I take quicker, smaller steps. While in heavy boots, I'm definitely a heel striker with longer strides.