Downoi, smaller crypts species, blyxia, stargrass, dward or regular sagittaria are all great foreground plants. I have all these in my low tech tank. No co2 or excel.
Good thought, then I would absolutely recommend dwarf sag and downoi.stargrass would require a bit of pruning =p and blyxa can grow really large without pruning so unless you have a 75g+ tank blyxa wont be much of a foreground
Staurogyne repens or staurogyne porto vehlo match your needs however they would need high light to be at their best but would still work as a carpet if you keep them thick