Golden Laced Wyandottes, Black Sex Links, Red Sex Links, Delawares, Cochins, Brahmas, and Faverolles are a few common, friendly breeds that would compliment your existing flock very nicely. If you want something a bit more exotic, look into Hamburgs, Polish, Sumatras, or bantams such as d'Uccles, OEGBs, Seramas, or Bantam Cochins.
Silkies do not get frostbite easily, mainly because they are so heavily feathered. Skinny, large combed breeds like Leghorns or Andalusians are much more susceptible. However, because of their small size and docile nature, Silkies can be open to bullying by larger birds. To some extent all bantams may face this issue, but Silkies in particular do not do well in mixed standard-bantam flocks.