I'd go with kuhli loaches instead of cories--they'll contribute less to the bio-load, so you can have 3-4 of them. Or, look into the dwarf cories. These little guys are a mid-water fish, that school better than many tetras. Very neat fish. Have 5-6 of them and nothing else.
White clouds are a good top level fish, but they don't do much. If you're looking for some activity, try getting a single, slightly larger fish. Paradise fish would be good (they won't need a heated tank, either) and are pretty with good colors. A betta is a classic standby, but will do better if the tank is kept a bit warmer (74 is the lowest I'd go with). You could have 2 female bettas instead--they're usually peaceful, and have the same colors, just not the long fins, of the males.
If you are willing to devote a bit more time to finding the fish, licorice gouramies or a pair of golden killies would do well in the smaller tank as well. Might be hard to find, though.
