Originally Posted by Bombalurina
I would always go for live plants - no harm can come from sharp bits! :) Anacharis, moss balls, java moss, anubias, ambulia, java fern and lacefern are all good starting points. :) Alternatively, if you have a facebook, search Acumen Aquatics. Those silk plants are designed especially with bettas in mind and are brilliant (I have three, plus 3 bits of decorations from them.)
+1 to this- as most of those don't need the substrate, some do better without it. As well as low light, and most of those don't even need a filter.
I say with plastic- any pointed plastic plant, regardless how small the points are, are fin damaging. But you do need a few plants at least in the tank, as being too empty could cause him stress to make him bite his own fins. Halfmoons are notorious for biting their own fins, so you will always have to always keep your eye on that. Sometimes it may not be the plants doing the damage, but the fish himself doing it to his own fins.