I know that we exist and I know that some things are good.
I would not say ‘things’ (material) are good. You can use ‘things’ for good and evil, but a material ‘thing’ is not comprised of good – i.e. money is neither good nor evil. I apologize if I misunderstood what you meant by ‘things’.
That being said, if we know that good does exist, where does good exist? It is not a material ‘thing’.