Your typical dual purpose breeds tend to be good foragers, rocks, Wyandotte, australorps, among a few, and most a decent layers. Light breeds too are great foragers, but they are a bit standoffish, but most lay well and tolerate the heat better. I like my Ancona and andalusian.
Easter eggers are great so that's a good start, though some aren't reliable steady layers. Most I've owned were great their first season but fell off in production pretty rapidly after that.
I would be interested is seeing your Cornish down the road. Are they the dark Cornish?