I may keep my eye open for a 1/2" thick piece of memory foam to put over the whole thing
From what I understand, memory foam isn't what you want, but rather, natural foam latex.
Memory foam takes a set, so when you move, the seat retains the shape of when you were just sitting for several seconds, so you tend to drop back to the same position you just were.
Latex foam "springs" back quickly, always re-assuming it's original shape, so when you raise off the seat or simply wiggle, the seat rebounds into the space that was just vacated by your sore ass, and gives you a "new" position.
I also heard that natural latex foam breaths, and memory foam is hot.
I'm no expert, so this is just my 2 cents, and worth maybe half that!