I keep Black Amazon Sword in two of my tanks, but not with my Oscars.
I tried and fatally failed (a literal fatality, for the plants).
In my 29USg bow Angelfish tank, I have a mixture of Sand and Eco-Complete. I use suction cups to hold them in place. You know the closed ring 1" suction cups used for holding heaters? that type, I slipped two or three leaves and placed as close down to the substrate as I could. It has been working wonderfully.
I believe that if you provide 2+WPG and DIY CO2 your Amazon Sword would make it, that's what I did.
Pepe
Santo Domingo