Of the three that you mentioned, I would say the Orpingtons are the most well known for docility.
You may also want to consider Red SLs (Gold Comets, Cinnamon Queens, etc). They lay eggs like pros and are generally quiet and calm (for chickens anyway).
I am wondering about a Orp with a flock of smallerish hens, I am hoping they will be ok together if I get them as babies. Does anybody else have experience combining Orpingtons, Polish, Silkies, Cochin Bantams, and Yokohamas?
I've got a mixed flock with a buff orp, a SLW, GSH, RIR, BR, blue cochin, black mottled cochin batam, EE and 3 black bearded silkies. I like variety, lol. They are all fine, though the ee and bmcb are newcomers but the others all get along. I think I just wouldn't have a single silkie. They hang in groups and are so tiny. I've got 1 pullet and 2 cockerels (THE 3 SILKIES) but the boys are just like the girls, if not, friendlier! Good luck! They are my new babies!
I have a mixed flock as well: Cochins, Golden Comets, Speckled Sussex.
From my experience, mixing breeds is fine UNLESS you have particularly aggressive birds mixed with gentle ones. My Comets are lovely girls, but they're a major pain in the butt every time I need to add new juveniles to the mix.
I really adore my Cochins- if you're just looking for the occasional couple of eggs and some friendly ladies, I'd recommend them. Orpingtons are better layers and have similar temperaments, but I think they aren't quite so cute. The Sussex are lovely birds but a bit more skittish than the others.
You'd do fine with any of the breeds you've listed, but like others have said I'd recommend keeping your flock at no less than three. They are highly social and need each other to feel safe and comfortable.
I have 20 chickens and 8 different breeds. I love the colors, different personalities - it's just more fun for us. Some are great layers, and others not so much but we love them all.