All these plants do well in my low tech tanks (no special lights, no fertilisers, no CO2);
cryptocorynes; plant in the substrate; different species have differing leaf shapes/colours
anubias; needs to be attached to rock or wood like Java fern. Again different species have different leaf shapes, so you get some variety.
bolbitis; another one for attaching to rock or wood; lovely and fern-like
aponogeton; nice wavy edged, strap shaped leaves. Plant in the substrate
Vallis (long, grass like, plant in substrate) is worth trying; it likes harder water on the whole, but does well in some soft water tanks
sagittaria; there's a giant one, like a huge vallis and a dwarf one that makes a good 'lawn' for low tech tanks (okay, a lawn that needs mowing, but 'proper' lawn type plants do need high light and CO2)
Java fern; two interesting variations to look our for are 'trident', that has deeply divided leaves and 'windelov', which gets moss like extensions on the leaf ends.
You want your lights on for between six and eight hours; any longer and, as Ch4rlie rightly says, you'll encourage algae.
Thank you, do you happen to know how large the plants get and can mossballs spread around by themselves?
Plants, in general, just get bigger and bigger. Elodea will get long, and Java fern will make big clumps. If they get too big for your tank, you can trim them. With elodea you cut the tops off, Java fern can be split by cutting through the rhizome (that's the thick stem that the roots and leaves grow from).
Moss balls won't spread, no, although you can pull them into pieces and roll them back up to make smaller ones.