Bass theme (on piano) throughout:

D  D E F  -- through first verse
D  D E F (G accents) -- through second verse
D  D E F (D G accents) -- rest of the way

The G accents get more prominent after the first chorus.

"But now...

Chorus:
G5   Bbmaj7    F
"Weeeeeeeeeeee'll float
G5   Bbmaj7     F
Take life as it comes..."

I think that Bbmaj7 is really nothing more than Dm with a Bb bass note (so Dm/Bb), but I 
play it as shown below:

Bbmaj7:  6x776x