I have been researching this same question. Only, I will have ADA Aquasoil as a substrate. At this time my opinion is that we are pretty limited if we want a low growing substrate, perhaps with Marsilea minuta being the only one that will reliably grow well and low. I plan to use Sagittaria subulata, but it will give me a "lawn" that is much more likely to be 3 inches tall than 1 inch tall. The usual low growing, carpet plants all seem to need more light and/or CO2 to do at all well at growing low and dense. I think most people who have success with those in "low light" actually have much more light than they think.