the best and most effective advice i ever followed for getting absolutely covered in poison oak was to go strip naked on my porch, wipe my body down using a bucket filled with cold water and a little bleach mixed in using a sopping wet rag, and then stand in a cold shower for a while. and wash the clothes separately a few times or toss em.
that was to remove the oil though and minimize skin contact.
once you're got, you're got, and after the oil is out of the equation and its more about managing the reaction, the pain, and not irritating your skin further. so i would do a lot of cool showers and antihistamine type shit. no scratch/no scrub, etc. the pumice is probably not the move to make.