I see some very eclectic mixes here with discus.
I tend to keep Discus with other warm water SA fish.
Some of the Tetras I recommend are:
Spotted Headstanders, Rummy Nose Tetras, Silver Hatchets, Bleeding Hearts, Pencil Fish and reluctantly, Cardinals. Seems to me many people who keep Cardinals with Discus are always having to buy replacements. I suspect they tend to burn out when kept in the med 80'sF.
Catfishes:
All the Hypancistrus sp, eg L260, L201 and Peckoltia sp. eg. L134 Leopard Frog Pleco, these all need warm water and eat same food as discus. Algae Eaters; go with Common Ancistrus BushyNoses reg or albino.
Corydoras sterbai
Cichlids:
Apistogrammas, Blue Rams, Keyhole, Wild Peruvian Scalare
Dwarf Pike Cichlids esp. C. regani, These rarely bother adult Tetras. A surprisingly good tank mate with Discus.