Another green cheek as a roommate (but not cagemate) would be a wonderful idea. In our home, we have 4 cockatiels, 2 green cheeks, 1 sun conure, 1 budgie and the largest bird is my bare eyed cockatoo. None of the different 'types' interact, except to fight or boss each other around. Its funny when everyone is out at the same time, its like little cliques, each group has their own area they picked (green cheeks on the big boing, cockatiels on back of sofa and table behind sofa, sun usually hangs out with a person and Ivory has perches, boings and toys on her cage and she is there or with a person and not the same one that the sun is hanging with).
The only one who is open to a friendship is my tiny budgie who has such a crush on the female green cheek. And of course she pretends he doesn't exist. Otherwise the green cheeks chase or boss around the cockatiels (they can't be on the same 'out' area), the sun and the male green cheek get way too beaky and dominance positioning. Poor Ivory being the big bird in the house is terrified of everyone and flies to a human for protection if anyone lands on her cage.
I know others have different birds that are friendly for playtime, and I know I worry, but my fear is the beak differences. The green cheeks could easily take off the beak of a cockatiel, the sun could do some serious damage to the green cheeks and probably crush the skull of a cockatiel and the poor budgie, well he's low guy on the totem pole, so everyone can eat him
Different variations of green cheeks are super cute together. We have a pineapple girl and a turquoise boy. We would never cage together, no babies for us and honestly the female would probably terrorize anyone who enters her cage, she is quite possessive of her home.
Good luck with your bird search!!