Your best bet would be to explore either a music theory textbook or musictheory.net, as they would give you a larger vocabulary for chords. Often times the best way to create a more melancholy sound has more to do with melodic implication than the chords themselves. For example, you cold write a bar in C major but have the melody follow an A minor trajectory, giving the ear a bit of confusion and surprise that the theoretically major chord has a sad side to it.
Also, check out chromatic mediants and minor IV/deceptive cadences in particular.
There's 1,000,000 ways to make a song sad, but those are just a few off-the-cuff thoughts! Try everything and never settle for less than the exact sound you want.