Playing jazz-blues: Scales for improvisation on standard jazz-blues progressions, walking bass lines for blues

What scales can you use over blues chord progression, for example over blues progression you use in your blues comping lesson (beacuse it is easy enough reharmonization of standard 12 bar blues to start with)? Which scale(s) to use over VI7 chord and other chords that are not in standard I, IV, V chords based blues? Where can you use blues scale in such progressions? It would be great to explain some basic bass lines for blues comping also.