Discus are SA cichlids.
I am guessing that your current stocklist is too "boisterous" for them, hence your distinction. Rams typically make good tankmates for them. I would avoid balloon ANYTHING like the plague- these are fish that are bred to be deformed. Fish farms/wholesale facilities breed to exaggerate and perpetuate this deformity, and essentially use the opportunity to charge a premium for breeding culls. You'll want to choose peaceful, passive fish that can handle the warm temps that discus like. I've kept angelfish with discus before, and for me it didn't work out in the long term. Some people report success, but you should definitely have someplace you can move angels to if the need arises.
One thing about discus that I cannot stress enough, is to start with good quality fish. They are worth the extra money and will save you stress and heartache down the road. Most of the discus you see at the lfs are poorly bred and already stunted before you even get them home. It would really be best IMO to source a good breeder if you want nice fish.