Crypts, Ludwigia, Swords and mosses are a good idea, Amazon Swords are probably the most common sword to find, Crypt Wendti is a good crypt and is also easy to find, Ludwigia Repens (Red Ludwigia) is a very easy plant to grow and is also easyer to find, Java Moss or even Riccia Fluitans are good low growing plants. Dwarf Hair Grass (DHG) Is also more or less easy to find and is easy to grow and if you are looking for a carpeting effect is a very good plant for that. Another Plant you might want to look into is Hygrophilia, Ive never kept Hygro. But ive heard it is somewhat easy to keep. If you are looking for a lilly pad type of plant you can get a Dwarf lilly ore even a banana plant (Banana Plants Grow lilly pads after some time).
Also Might i suggest getting C02, It is very simple to DIY and really helps plant growth, Also if you dont have a nutrient rich substrate you really need to start dosing some ferts, All plant carrying LFS's should carry some sort of liquidized fertelizer as well as root tabs to place under the substrate of your tank.