Have you allowed the nylon to moisture condition to a reasonable ballance with the atmosphere. It's dry fleural modulus can be up to 3 times as high when dry vs conditioned.
If the nylon is conditioned, try LDPE modified nylon 6, which is sold as a cheap toughned grade, or try MDPE.
Some rubber modified PP, such as auto bumper grades might be of interest
It depends a lot on why nylon was chosen in the first place, and what other properties you need.
Also, mould shrinkage is not quite that simple. Two different materials might have similar shrinkage in one mould, but different shrinkage to each other in another mould Regards
pat