Yes, I use the original chords also, except for the Gb maj7 in the first chord of the bridge. I play it as a Bb min6. On the next chord (B7) I play a fill with a broken chord of 9ths and flatted 5ths. With the D7 I use a whole tone scale for the fill. The Eb7 chord= below it add a flat 7th, flat 5th and the Eb root note. The D7-9..who figured that one out? I play the chord thus: going down from the melody note G#, E, C, F# (it's a D7 9th-5th. Same with the C7. Play it as a C7th flatted 5th on top and E note on the bottom. Easier to play it then explain it.

I was never much on "chord substitution," but the fellow I was studying with last year introduced me to it on a surface level. A month or two ago, the penny dropped and I found out I just love the dissonance I'm hearing now compared to the standard chords: 6th's, major 7ths, 9th's. Just the flattened 5th alone (against a 7th etc) makes a world of difference in the overall sound.