Sounds right.
Problem is, AFICT, podiatrists typically commonly use polyurethane foam as the liner when making orthotics - because it is very durable. So that's what I wanted to imitate.
If you're really concerned about skin contamination, you can stick a layer of moleskin on top of the foam liner. The Dr. Scholl's and Curad brands last at least a year under my skating conditions (5 sessions/wk; 1.5 hrs/session; almost yr round). When the moleskin wears down, and if the underlying foam is still good, you have two options. With some foams, you can strip off the moleskin without damaging the underlying foam, and apply fresh moleskin. With other foams, you can't. In which case, since the moleskin is thin and squishy, you can simply stick a second, fresh layer of moleskin on top of the first, worn moleskin. When the second layer of moleskin wears down, you can strip it off the first layer, and apply a fresh layer.