Hi,
What strains are his goldfish? What size is his tank? Most strains can be a little more feisty than another but it also comes down to personality. There isn't a shrimp that will happily live with goldfish except if there is enough hiding places for it to seek refuge, should the goldfish attempt to peck it. Bamboo shrimps may be your best bet.
As for snails, there are plenty of snails that will work quite well. Nerite snails, trapdoors, trumpets and apples can but please make sure first your goldfish will not attempt to peck them. Flaringshutter keeps her shubunkins, comets, hybrid koi/goldfish named Sygnus and other strains with her Pomacea haustrum, Melanoides tuberculata, Pomacea canaliculata and a few other apple snail species. Mine are with a lone cana I am testing at the moment which they ignored completely. Ramshorns, bladder snails, pond snails and trumpets stand a better chance if they sustain their population properly in case your goldfish have a taste for snails.