What specifically are your objections to a rooster? There are a whole lot of myths going around on this site about them. There are considerations and risks when you have roosters, but many of us have roosters with our flocks and the world as we know it has not yet ended. How much space you have and how many you plan to keep will also enter into the equation.
The risk of bringing in a rooster to your flock for a short period of time to get fertilized eggs is the risk of disease or parasites, both the risk of him infecting your flock or your flock infecting him. If your flock infects him and he carries that back to his home flock, the other flock owner will not be very happy. If he is coming from an established flock that has not had contact with other chickens for a few months, quarantine will not do you much good. He is probably already immune to any diseases he might be carrying so he will not show any symptoms in quarantine. It will give you a chance to look for and treat for mites, lice, and worms and there is always the possiblity that a wild bird has recently infected the flock with some new disease, so there is always the possibility that something will show up. If the other flock has had contact with ouside chickens recently, then I think quarantime is a great idea. With quarantine, I think it is a good idea to put one of your chickens with the new chicken in quarantine to see if they infect each other. That way, if he is carrying a disease that he is immune to, you will only be putting one of your chickens at risk. If you read this closely, I am not saying that quarantine is not worth doing. What I am trying to say is that for it to be effective, you have to put one of your chickens with him in quarantine for it to be effective because of the immunities flocks sometimes develop.
If you do add a rooster to an all-female flock, add an older rooster, one at least a year old. That way the rooster coming in will probably be mature enough to dominate the flock immediately. There are no guarantees because thay are all living animals with their own personailties and anything can happen. I've had roosters at 15 weeks of age that dominated grown hens, but what will often happen is that the mature hens will not accept the dominance of a immature rooster that does not have the strength of personality to dominate them. They will beat him up unmercifully until he gets old enough to dominate them by force of personality. He will have the physical strength to force them, but many will actively resist and it is not pretty. Sometimes one of the hens has taken on the role of the rooster as far as flock dynamics. She may vigorously resist giving up her flock dominance role. Your odds of this going smoothly increase greatly with an older rooster and usually introducing a mature rooster to a flock of hens does go very smoothly. With a mature rooster, it is not the pecking order that changes. It is the flock dominance position.
If you want a self-sustaining flock, you have to have a rooster. It is possible keeping a rooster is not the right answer for you. You may want to learn artificial insemination techniques and find a source for the sperm.
With a small flock and the breeds you are looking at, it is hard to depend on a broody hen to hatch and raise repalcements. In all honesty, you are probably looking at an incubator.
Hope this helps a bit. Good luck!