a planted small java fern (which btw doesnt do so good)
^ It's isn't doing so good because
Java fern is an epiphyte - it grows on rocks, wood, like an orchid. Planted in the substrate, the rhizome will rot and yeah.. not so good. Pull it up and tie it to a rock or driftwoood by the rhizome with cotton, drop it back in. Give it a few weeks to recover, it'll be fine.
Anubias is another that grows well on wood or stone.
If you have lighting that's fine for plants, you could add some more clumps of java fern (the narrow leaf one is spectacular..) , banana lilies (nip the really leaf stems off to keep them thriving, float the nipped leaves for new plants..), elodea, hornwort, wisteria, peacock moss .. just try stuff. If it goes well, it goes well..
Some plants, however, like bulbs, lilies, swords, anything that isn't 'stemmy' so much as rosette or dense-rooted (root-feeders)- might need fert tabs around their roots now and then. I dose a little Flourish (NOT Excel) once a week, fish poo does the rest, for the stems (water-column feeders).
As for stocking.. if you're planning the tank around the betta, go for schools of peaceful fish that aren't long-finned or very colourful. Make sure the fish don't need high water flow (like loaches! <-- I learn by error..) or cooler temps than a betta likes.
I have a bristlenose catfish in with my wilds, so far so good. I know OldFishLady keeps community tanks, she'd be good to ask.