What people fail to say when they claim to have males/females together is that they live in harmony for a week.. possibly two.. or even less. Most people post their "friendly" fish just shortly after introducing, but fail to say that a week later one or both is dead.
It IS possible if you have the right temperamental bettas, and a very large tank (55g+) that is extremely heavily planted. One member here is successful with it, but that is after generations of siblings and trial/error.
Would be nice if it were possible.. would solve a lot of my space issues :D lol
But everyone here has you covered.. sorority of 4+ females (based upon size of tank), lots and lots and lots of plants mid - top level.
Good luck :)