Foundation repair: time frame
If it were me, I'd stick with your drainage improvements, monitor, and save pennies to fix this for real.  1920s-and-older construction is often significantly overbuilt (I've owned 5 so far, so take the sample for what it's worth statistically!) and can take a lot of abuse.  You do want to fix this, but your time frame seems to be in months, not years.  If you see shifting measured in millimetres, given the tectonic rates at which houses shift, you're probably ok for the next couple years.  If your monitors show issues, move fast.

All of that is provided that you are not talking about significant (recent or contemplated) excavation, changes in the surrounding water behaviour (did you remove any trees?), and that you are getting the water far away from the foundation.  Stabilize all that, and I bet you'll be ok for the next few years, assuming you have no seismic problems locally.  

Also, of course, this advice is worth what you paid me for it; if you'd paid me, I would't give it. :)  But that's what I'd do.