Here's the bassline for "Happiness Is A Warm Gun". Nothing complicated from a technical standpoint, but it's a really interesting song because of the many meter changes it has. There are lots of cool stuff going on there, like the final 3/4 section in which the whole band is playing in such meter but Ringo keeps pounding in 4/4. At some points it seems that the bassline was doubled an octave higher by a guitar, so I added some octave double stops where I judged them to be appropriate. And yes, there's a low C at the very end of the song.
Happiness is a Warm Gun (Bassline)