I have Crypts, anubias, java fern, fava moss, hygro polysperma, hornwort, duckweed, frogbit, guppy grass all in 1 wpg and all are growing.
CO2 doesn't become a necessity until you get into the high light where without it, you will be growing a lot of algae. Snoopy suggested a lot of good plants for 1 WPG, go with those.