I think you are off to a good start. Your plants look pretty healthy. What are your tank conditions, lighting, fert regiment, etc? H. zosterfolia would be nice substitute in your tank for the Hygro polysperma. I am not sure aht you man by stable, most of these stemsare fast growers, but its hard to get most of the hygros for look bushy and full. Usually they have long internodes and can look leggy, plants like Stargrass and Rotala green might work better for you here as they can take on a bushier apperance.
Try creating more foreground, it will give the tank depth and make it seem neater, even larger, than it is. Loose the ball of moss in the front. the riccia is nice but htere needs to be more foreground. I see you have soem tenelus of rostrate in the forground, spread that our and make a nice little "meadow in the center, off center. That will compliment the concave/ sort of double triangle scape you have going already. I have often wanted to try a scape that has 2 triangle layouts, one disappering behind the other but have not had the tank or sucess for it.
I think the last thing to work on is trimming and pruning. Learn how your plants respond to trimming, and try to shape them into more orderly groupings. Post more pics