I recommend cabomba, its my go to plant. Grows in any condition, soft and makes a nice bed. If your in Canada you can order them from the plant guy
, he got nice plants and is a very nice person.
If you want a heater, you try the elite 25w heater, I use it in my 2.5 gallon and its great. Its adjustable, it shuts off and on depending on the water temperature. My is set to 78F and it doesn't turn on during the day because its so hot, but at night, it turns on a few minutes to make sure the temp stays at 78F. I got my at pet supply store, but if you can try MyPets at the west Edmonton mall, I remember seeing a store when I visited. I'm sure Edmonton got lots of pet supply stores so you probably find it.
You don't need soil, gravel works just fine for plants. Without some sort of bubbler and lots of water changes, soil can become anaerobic, it needs lots of research so read up before you try soil, especially in a tank without a bubbler/filter.