12.40Make a ballad progression richer

Basic:

C | Am | Dm | G7 | C

Version 2:

C | E7 | Am | A7 | Dm G7 | C

Version 3:

Cmaj7 | E7 | Am7 A7 | Dm7 G7 | Cmaj7

Now voice it smoothly.

You're getting very close to a classic standard-style harmonic vocabulary.