Personally, I get some stems in there for variety of texture and to fill in the back of the tank. Maybe some hygrophila or bacopa. I'm a fan of myriophyllum at the moment for some reason too and it'll give you a different texture to play with.
I agree with the carpet idea. Maybe some pogostemon helfrei or some staurogyne repens in a patch with some dwarf hairgrass.
Thanks for all the suggestions guys, much appreciated. The lighting isn't too good so I think i'll go with some hairgrass, 3 more java ferns for the wood and some amazon sword. Thankfully the vallis has also thickened out since the pic. Thanks again- I'll post a pic of the updated tank when I get the plants