Would you be able to post a pic of your tank? There's so many options, I think it will help narrow things down so you get the best for your current set up
Without a picture, amazon compacta, red rubin sword, kleiner prinz and kleiner bar sword are some of my favorite smaller sword plants that can work well in the background.
Dwarf sag or the shorter variety of jungle val are sea grass looking plants.
You can use plastic mesh and your java moss to make a moss wall as a background.