Would silkies and/or polish be good fits with them?
Thank you for listing them. For the most part it seems you have a fairly docile collection.
Regardless, Silkies no matter where they are will be at the bottom of the pecking order and MAY face a bit of bullying. If you're going to introduce new chickens the polish would seem to me to be the safest effort. With introducing Silkies I'd have to admit I would be hovering around the run frequently.
I had to nurse a Silkie back to health from a severe beating from a roo years ago. I have a buff polish roo now, we decided to introduce 6 pullets to the flock of 6 and it's worked out very well. I have a Brahma roo and 2 hens (all young) that we house in another run....I'm growing monsters!