I buy Superfeet Green Wide insoles and trim them down to the width and length of the original boot insoles. Great fit and no slop. If your feet aren't wide, then try one size up in whatever superfeet insole you prefer. The caveat is that the arch support is proportionally larger with increasing insole size.
I've had bad (as in debilitating) plantar fasciitis (and Achilles tendonitis at the same time) in the past from running with ice spikes on my shoes and was able to resolve it by:
1. Regular rolling of plantar facia on a lacrosse ball
2. Stretching toes to improve dorsiflexion
3. Stretching calf/hamstring - weighted Jefferson Curl stretch with wedge/ramp under toes
4. Strengthening tibialis muscles to balance out over-worked calves.
5. Strengthening Achilles tendon with weighted eccentric calf raises and isometric holds
6. Stretching calf/Achilles tendon with isometric wall stretches and "ass to grass" lunges, pushing the lead knee forwards of the toes.