Blues harmony is very much up in the air...
As a starting point, I'm usually working loosely around either the major or the minor pentatonic - which depends on the "feel" of the piece and the mood I'm going for. That said, this is VERY much just a starting point. One, you're going to be throwing in a lot of outside notes, and two, there's no reason you have to stick to one (more later).
Next, remember the two basics of blues harmony. First, it's largely about so called "blue notes" that fall between pitches - in particular, the minor and major third, but also to a lesser extent the minor and major 6th and blurring the line on either side of the flat 5th with the perfect 5th and perfect 4th. Second, it's largely based on 7th chords - even if you're soloing in a "minor" feel, the odds are good that the implied harmony of a one-four-five progression is really I7-IV7-V7.
So, start off your solo... But remember that if you need chord tones to resolve to, if you're playing in E, when you're on the I chord dropping in a major 3rd in a minor run and a minor 7th in a major run is totally fair game. For bonus points, try bending the minor 3rd anywhere from slightly sharp to all the way up to major. When you hit the IV chord, again, think in terms of a dominant harmony - if you're playing in E with a minor feel, the C# (the major 3rd of A) is now a great "color" note.
Another thing to keep in mind is that there's no reason you can't move between "major" sounding passages and "minor" sounding passages in the same solo to add tension. One of my favorite examples is Jimi's excellent instrumental cover of "Born under a Bad Sign." Listen to it - for one, I think damned near everything you need to learn about modern electric blues can be deduced from this solo, but in particular he really gets a lot of mileage out pushing the tonality. In particular, the second chorus, starting at 0:48, is fascinating - he's pretty rooted in the minor key for much of the chorus, with a brief nod to major around 1:06 or so, but then he hits the turnaround at 1:11 or so and goes into very major territory, which contextually sounds VERY tense against the V7 after establishing such a solid minor feel (worth considering - this is in B, I think, and the M3 in B is D#, which against the F#7 is a major 6th), before closing the turnaround back in minor. It's absolutely brilliant.
Anyway, some thoughts... Basically, this doesn't sound helpful perhaps, but it's really not so much about scales. Think about chord tones, think about tension and release, and let the scales follow from that, but only look at the scales as a rough outline, and don't feel the need to stick to just one.The nice thing about blues is it's often pretty sparse so it gives you plenty of time to think about how you can add and bring back in slightly tense notes.