's W toggle is meant to do exactly what you need, at the time.
Most people use blood prince after landing a Q into W, then switch to blood thirst once you get a little low.
Also, consider maxing W first, it offers you a lot of sustain and pressure in lane.
Charging up two stacks and swapping to blood prince for a quick Q/AA disengage with E will leave you relatively un damaged while doing a large amount of burst damage to your enemy.
Using lifesteal quints combined with a dorans blade for a total of 6.5% lifesteal at level 1 is key to sustaining in lane long enough to outfarm your lane opponent, and get ahead.
I also considered using attack speed glyphs(5) and scaling MR glyphs(4) for setting off your W as much as possible. Rushing
then
OR
vs AD/AP respectively. Will make you an automatic non-target in teamfights. But you'll live long enough to kill any carry or at least make sure that you do enough damage to really help your team.
Mid game aatrox is a splitpushing machine, and this is how you should use him. Push your opponent out of lane and get big by farming up and taking turrets,
into teamfights when you need.
Hope this helps!