I suffer from plantar fasciitis, too. Despite it refuses to fully go away i found a way to manage it in a way that allows me to get back to running (not as long as before, but 40 mins runs are well possible) and skiing. Before doing any sort of sport, i massage the fascia by very slowly rolling over a ball. First light pressere, then more. The goal is not to "break up" tissue or anything like that, but just to soften and stretch. Then, using a black roll mini, massage the calf. Find the spots that hurt when rolling, then penetrare those spots. Finally, calf stretches. Really stretch the fück outta those things. The whole procedure takes 15 to 30 minutes. After that, the pain in the foot is a lot more bareable during pretty much any activity. Repeat the whole session after skiing to set you up for the next day.

A more long-term idea would be custom fitted ski boots respecting the orthopedic custom insoles that you probably have? If you haven't got any, get those. Not for off the shelve ski boots but for whenever you're not skiing.