Hi personally in my discus tank i have three albino catfish and they are doing very well and growing up fine. I also had a panda catfish but i found it dead this week. But i do not know if it died resulting from high temperature or not. It seems this week the temperature has gone down and the water is cooler.
I would like to suggest the congo tetra as it grows up to a nice size and is safe from the mouths of discus. I also have the black phantom and rummy nose tetra. Besides that i have three large clown loaches. Some people say that clown loaches can harass discus, however so far no trouble, I also have a couple of bristle nose.
You can also keep ramerezi in the tank as well
Frank