http://www.torvund.net/guitar/BluesG...around_1-1.asp
thats the site i use for anything like that i need, with a link to the blues turnaround lesson already. its for guitar, but the theory is the same for bass. iin its most basic for, its simply an authentic cadence with just a V7 to a I but they explain how to use diminished chords to make it more interesting and lead better. Dont freak out with the chords, it shows examples and you can listen to midis of them and it has music. just look at the chords, and you can use notes from there and itll work sound decent. try just using the tonic first though, itll make more sense. hope this helps, if not say so and ill try to explain it more for you if the sites not good for you. keep rockin