All filters are actually good for discus fish.
No filter is specific only for discus fish.
Filters are used for filtering water to adjust the water quality to suit the discus fish.
Small quantity water needs smaller filter but if water is dirty it needs bigger filters.
If you want live plants to decorate the tank, you will put gravels to grow the plants on it so you need under-gravel filter.
There are many different types of filters. You will pick one that will serve your purpose.