Basic bass notes for the first part:
Oh-E
Oh-Db
oh-B
Oh-Ab
oh-A
I'm - B
Grateful - E
repeat
Verse (sorry I don't have time to try to match the words to the notes):
A (first time)
Ab
Gb
B
E
E (walk-down to the A)
Eb
Db
B
A (Second time)
Db - (walk-up to the Gb)
Eb
F
Gb
B
E
repeat as necessary
Hope that helps a bit. Listen to the vocals and what-not to fit the chords to the bass.
