hmmm. I think you may need to think outside the box a little. Maybe make your own pad or lift your fone pad up and place a 1/2" eva foam insert under it for extra softness.
I think you may need to explore board options for to get a smoother board and also consider the power you hold down. The more power you are holding the harder it will be on your feet. I can blow my heals out in a couple of hours riding super powered on my speed 3, but spend many hours correctly powered on smaller kites.
North did this with their pads and I have them on my Cabrinha Custom and there was not a noticeable difference versus the FOne pads. The FOne pads were still softer so I immediately ruled out doing this but thanks for the suggestion. As far as exploring board options I am at the the limit for comfort with the Cabrinha Custom. It is a very forgiving board and has plenty of rocker to make chop seem like it's not there. And no way am I gonna' trade off for less power.
I realize my riding style limits the level of comfort I can expect but the point of my post was not about compromise. I'm simply asking for feedback on the softest pads on the market.