Java fern is another plant that can be tied or glued to something in the tank. I glued mine to tiny terracotta pots. They have now grown enough to completely hide the pots. I have both regular java fern and also the windelov type. I too have a hard time keeping lots of different plants growing well in my very soft water but the java ferns do really well.
Crypts also do well for me as long as I keep them away from my rabbit snails. I do plant my crypts. They are normally tough plants so you may want to consider them if you've not already done so.