I understand where you're coming from regards the treatment of chickens, and other animals in general. Unfortunately there isn't a lot we can do short of farming our own animals. And that just doesn't happen in the cities.
Starving yourself of animal products like eggs and milk won't stop the cruelty. You need to get governments involved and change the laws and legislation. Become a pest to them and write letters explaining your viewpoint and what you believe should be done to help minimise the trauma associated with these industries. The government will write back a few months later saying blah blah blah, but if you persist and respond, and keep putting forward your ideas, things can change. If does take time, years in fact. But it can happen. You need to be logical in your argument and provide realistic alternatives to what is currently being offered. If you can do that then you have half a chance at changing things.
Regarding space or lack of it in your garden. Japanese quail aren't that big. About the third of the size of a normal chicken. A 10x4ft run would be fine for a few of them. You can have plants in with them and they will pick at the leaves and keep insect pests at bay. And because they are ground dwelling birds the cage/run doesn't have to be that high. They can fly a bit if startled, like any quail, but they usually go up and come down nearby.
The other option would be bantams. These are half sized chickens that are more suited to small environments.