I agree. Great suggestions, Donrae! If I may, I'd like to add the Sussex t that. A brown rooster over a Light Sussex hen will give you sex-linked colored chicks where you can tell the boys from the girls when they are chicks by their color. It works because the Light Sussex is a silver bird. ( it does not work if you use a Light Sussex rooster over a brown hen.)
Yeah, silkies and Polish don't always do well with the big girls. Best to keep like to like, if you want ornamentals house them separate and they'll do better as a rule.
With the flock you have now, any dual purpose bird should fit in nicely. You could go with a darker brown layer--Marans, Welsummer, etc. You could add some different colors/patterns--Australorps, barred Rocks, buff Orpingtons, silver laced Wyandottes. It's really up to you and what you have available, but anything marketed as a heavy breed or dual purpose will live well with your current flock.
