Definitely tons of Java fern mat. It is legit foolproof and extremely low matinence and doesn't require any special treatment or even to be planted in substrate. You can just tie it down to a rock or
driftwood or superglue it, or do what I do and just stuff it in the cracks of stuff to pin it down. It will take a few months to really take off (it still looks great when first bought), but boy it will explode over time and reward you with a huge beautiful bush of green leaves with minimal effort required. I would also suggest various anubias species, same exact deal as the Java fern no different instructions for care/planting which is nice. I would suggest the coffeefolia variety, the leaves grow large and would look great in a big 75.
Here is my 29 gallon with Java fern, and the anubias coffefolia is the largest leaf anubias you see in the tank (left and right of the center drifewood) mind you, i like simple, so I do not use any ferts, fancy lighting, substrate or
co2.
Java fern and coffefolia when first planted:
View attachment 756406
About 6-8 months later:
View attachment 756407
About a year after planting:
View attachment 756410