I second getting anubias. You could try getting some water wisteria or anacharis for larger background plants. Pennywort (Hydrocotyle leucocephala) may work as well. You could also do some floaters like frogbit?
What companions will work for a betta really depends on the betta's personality. Generally, corys, otos, and snails are recommended. Gouramis & showy guppies are not recommended.