I wouldn't put a gourami and a paradise fish together to be honest. They're similar 'types' and you may have territory issues in a small tank like that.
You could put a molly in but if I were you I would make SURE you get a male. Even on it's own a female can give birth up to 3 times with stored sperm.
Alternately you may want to instead get another skunk loach or two. Loaches are VERY social critters and it's recommended they're kept in groups of three at very minimum.