The chocolate gouramis inhabit the same areas as many of the acidic-warer loving Cryptocorynes. I would try those Cryptocorynes coming from the same general area as the chocolate gourami (southeast Asia), including such plants as Cryptocoryne cordata var. blassii, Cryptocoryne pontederiifolia, Cryptocoryne albida, et al. I would pick one or two of the Cryptocorynes for the right side of the tank. As for the left, some plants that may work include Cryptocoryne ciliata, any marginal house plants (like those palm trees they keep seling at the fish store) that don't mind having their feet underwater could be used to good effect.