There are two things I'd consider before I even thought about breed. First is how much room you have. I don't just mean in the coop in isolation, but how much room total they have in coop, run, and maybe free range. When it is available is important too. It doesn't do any good for them to have a huge run if they are locked in the coop alone when they are awake. Allowing them to free range one hour a day doesn't help the rest of the day. When they are asleep it doesn't really matter but it can when they are awake. During integration you need even more room.
The second thing to consider is age. A mature hen outranks an immature pullet in the pecking order. I don't care about size of the individuals, I care about maturity. It's not that unusual for a bantam to dominate a full-sized hen if she has the personality. Normally a pullet is mature enough to enter the pecking order if she is laying. Until she is laying treat her as an immature chick, which requires even more room for integration. I integrate young chicks all the time so it can be done, but it does take more room.
As to your question, which was about breed, I'm not a big believer that you can predict the behavior of one or two hens based on breed. Breeds have general tendencies but there is a tremendous difference in individuals. You have to have enough of any breed for averages to mean anything, the individual differences are that strong. You mentioned yourself the differences in personality of your current two. I also believe the more room you have the less important those differences are.
Different flocks of the same breed have different tendencies too. Flock or breed tendencies are handed down partially by genetics. If the person selecting which chickens get to breed uses behaviors as on of the traits they select for you can develop a flock of any breed that's generally pretty laid back or generally aggressive. There is still going to be a lot of variation between individuals in any flock of any breed but you can have a flock of RIR, Barred Rock, or Orpington that is generally aggressive or generally laid back. You can have a flock of any of these that go broody a lot or that seldom go broody. Selecting based on behavioral traits is how breeds originally developed breed tendencies.
I have a lot of room and don't worry about potential personality conflicts based on breed. It's been a non-factor for me. I don't know what breeds are available to you and I'm not sure what traits you are looking for in your chickens. I'll assume egg laying. In that case I'd want a full-sized chicken, not a bantam. I'd want one that is not known to go broody a lot, they are not laying eggs when broody and they take extra management. Orpington are known to go broody but the two I had never did.
I don't know what other traits you are looking for or your general climate. Some people want pets they can cuddle so flighty birds are generally not good. Some birds do better in cold or hot climates. This type of thing could influence me in selecting breeds more than whether they are supposed to be aggressive or docile toward other birds.
Going through Henderson's Breed Chart is a great idea to help you select breeds you might be interested in. I'll give you a link. Knowing nothing about your climate, goals, or management techniques it's kind of difficult to make suggestions but I'd start looking at any of the Rocks, Wyandottes, Delaware, Buckeye, Dominique, Dorking, Leghorn, New Hampshire, Sussex, Marans, Welsummer, or maybe Chantecler.
Henderson's Breed Chart
http://www.sagehenfarmlodi.com/chooks/chooks.html
Good luck! In many ways it's hard to make a bad decision.