Cochins do reasonably well in dry heat. If you are especially worried about the heat get a lighter colored bird as no matter the breed/species (kanine/feline/equine/bovine/goats/swine/poultry) lighter colored animals do better in hot weather. AND!!!
Brahmas, Orpingtons, and Wayandottes are all great breeds that will get along fine with Silkies. Australorps are beautiful birds but like to dominate smaller birds.
Cochins are also very friendly docile quiet birds, standards lay medium to large eggs, and bantams lay small to medium (same as...