What fingerstyle blues sensibilities I possess are more than somewhat the result of two formative sources from my teenage years, Richard Saslow's book The Art of Ragtime Guitar and Stefan Grossman and John Renbourn's second duet record, Under The Volcano. More to the point, Saslow's "Bloozinay" and Grossman and Renbourn's version of "Mississippi Blues" were how I learned to think about playing blues in the key of A, even though I've since forgotten most of Saslow's three beautiful choruses and I didn't learn "Mississippi Blues" properly for more than twenty years, and even now it's a sometimes still a stumble to play it just so.
I learned about 9th chords and the sound of D7/F# from Grossman and Renbourn, and about walking bass lines and chord subsitutions from Saslow. The idea of a scripted three-chorus blues also inspired my own "Weekhawken or Bust" from my record Plays Blues, Ballads and a Pop Song (and which I teach on my Truefire New School Fingerstyle Guitar course. But I digress).
The following 12-bar solo is a bit of a riff on all of that. It's got half-time alternating and walking bass lines, 9th and 6th chord voicings, double stops and harmonized blues licks, and chord substitutions with altered tones, among other things. I've included both notation/tab and a moderate-tempo recording of the whole thing, so you can take your time and work through it at whatever pace you like.