I personally never had much problem with the Jackson Happy Feet except that after a year or two, the air bag portion started not hold air well, just due to wear and tear. I would go with minicell foam.
To determine the shape of your foot brace, take the front pillar out of your boat and tightly compress a whole bunch of aluminum foil in the front. Get in and put in your feet in a comfortable position, adding more foil if you need to. Once it feel just right, pull out the foil and you will have a model of the shape you want to aim for when carving the minicell. You'll probably need one or two 1'x1'x4" blocks of minicell, or if you have bunch of minicell scraps floating around (like I did) just glue them together with contact cement. Serrated bread knifes are great for making the bigger cuts and a curved Sur-Foam is the best tool for shaping the foam.
Have fun, it isn't hard to make at all.
"It's All Good"