I wouldn't call that a key change, unless the C major chord is held for half a minute or something. :) It's simply a temporary scale or mode change, "borrowing" a V-I (or V-i) motion from F minor. In the key of F minor, the dominant-tonic chord combination is C7 - Fm. You can expand on that idea by playing a Bbm or Bbm6 chord on top of the C major - that's even more stuff borrowed from Fm key, like iv-V-i from F minor.
There's one thing that won't work, and that's trying to fit any single scale on top of an entire progression like that. It's better if you can twist the modal feeling elastically all the time, and you already found out that your chord progression moves through different harmonic feelings, so there won't be any one-scale-fits-all solution.
Edit: I forgot the dreaded pentatonics. For example C minor pentatonic might actually fit over everything - but to my defense, the word "pretty" was mentioned in the question, so that rules out a pentatonics-for-them-all approach. ;)
Some scale ideas for each chord
- Cm : C natural minor, C harmonic minor, C melodic minor, C dorian, ...
- G7 : C harmonic minor, C melodic minor, G half-whole diminished,
- C : F harmonic minor, F melodic minor, C half-whole diminished
- Fm : C natural minor
- A♭ : C natural minor
- Cm : same as before
- G : same as G7
- Cm : same as before
However, instead of playing entire scales, overlay or outline other chords on top of the backing chords. The other chords inevitably create some scale/mode feeling. Here are some ideas for chords to outline:
- Cm : (alt. 1, C natural minor) : all diatonic triads in Cm: Cm, Ddim, Eb, Fm, Gm, Ab, Bb
- (alt. 2, C harmonic minor) : Cm, Fm, G
- (alt. 3, C melodic minor) : Cm, F, G
- (alt. 4) : Cm, Db
(alt. 5) : Cm, D major
G7 : (alt. 1) : Cm, G, Fm6, Ab, Bdim7
- (alt. 2) : Cm, G, Bdim7, Fm6
(alt. 3) : Bdim7, G, E, Db
C (alt. 1) : C, Db, Edim7, F, Bbm6
- (alt. 2) : C, Bb
Etc. I may have made some mistakes with the chord list, but the point is that instead of first deciding an entire scale and then playing notes and chords from that, you can play chords without thinking so much about the scale. Who cares what scale it is - you cook your own scales and change it all the time. On top of a backing Cm chord you can overlay ... Eb, Ddim, Dm7, F, Gb, A, D7, Db, Adim, G7, Bbm6, ... each of these creates a feeling and changes the mode very elastically. Someone might say, all the chords are "from" a scale and in a way it's true, but another perspective is to say that combinations of chords create a scale.