I don't have any advice on a betta sorority, but I am into easy plants. Some that work well for me in low tech planted tanks with good lighting, and little to no ferts, are dwarf sagitarria, rotala indica, crypt wendtii, and hornwort as a floater. Obviously anubias and java fern are great but are very slow growers so I would use them in combo with some fast growers as well for nitrate consumption. The sagitarria and rotala love my black sand also, and spread much better through it compared to my eco complete.