You're right, the next logical step would most likely be "How to Jam the Blues Alone" (HJBA), you might also want to look at "Acoustic Blues Guitar Unleashed" (ABGU), which is Griff's acoustic version of "Blues Guitar Unleashed" (BGU). ABGU and BGU are more about skills and learning a breadth of techniques. One if obviously more focused on acoustic guitar playing, there will be a lot that is common to them, and stuff that is not. Both would be useful to you regardless of whether you favor acoustic or electric blues. HJBA is more focused on giving you the skills to outline a blues rhythm in a few different methods and keys and to comfortably drop in one and two bar fills. I'm moving through that and have done most of the first three sections and they are a blast!
Hope this helps.