Java mass can be rather difficult to obtain a carpeting effect but it can work with some diligence. Unfortunately almost all of the carpeting type plants that you see out there require higher light and benefit greatly from CO2 injection. Some of these species can be grown in lower light, but they won't carpet well and instead will grow up towards the light instead of spreading out along the substrate.
One exception might be Echinodorus tenellus which can grow under lower light conditions, albeit very slowly. It also is a bit taller than the traditional carpet look, but can work very well in a low tech tank.