NTRU is likely the most accessible post-quantum crypto as it resembles RSA on convolution polynomials, if you squint at it. It's security is based off of Lattices (integer coefficient subspaces).
This one looks like it requires only a (slightly advanced) undergraduate level in group theory, but there are big gaps from being just slides. Of course, I could actually only think I understand it and be completely wrong. ;)
The slide I referred to mentioned the instantiations, not all of which provide pfs.