Aside from mounting a regular (i.e., longer) Stick on a stand (which I've done and am prepared to do again), the Alto seems like the natural solution for a guy with a lower back problem.
However, the low end is sacrificed - something I think I'd miss.

Does anyone have any experience with an octave pedal which truly lowers the sound of an instrument by one (and/or two) octave(s) but retains the original sound?
I tried the boss version with a guitar, but found the sounds it made to be quite nasty.

Is there anything I could plug the bass side into (without MIDI) and get a true octave drop, without the usual replacement of tone.

Thanks.

None of the octive peddles I've tried were any good. They weren't natural sounding.

I agree that an octave shifting effect is not going to sound very natural, in that case a GK equipped bass side and a Roland VG would be the best bet for pitch shifting.

A couple other thoughts:

I believe the lowest note you can get on an Alto is low F above low bass E. If you've listened to any of my music examples, I tune to a low bass E and don't think I give up much low end. With thinner gauge strings you won't get as "thick" of a tone as you would with normal bass strings, but some EQ could help with this.

Regarding back troubles, have you played seated much? With a loose belt and the belthook rested on the end of a chair (I use a keyboard bench with a flat piece of hardwood going across it, and a notch carved out of the wood for the belthook to pop into) virtually the entire weight of the instrument is transferred to the seat.

Thanks (to you both, so far).

Rob, do you mean low bass E on a bass guitar, or on a guitar? If bass, that's surprisingly good news.

For my back, I have made a wooden square - four and a half inches square and half an inch thick. This has L brackets on the bottom - a half inch side. The other legs of the Ls then screw into a mic stand with holes drilled into it. I then use a peg-hole system to pin the Stick belt hook in place through the exposed adjustment holes.
Works quite well, if slightly wobbly, but I keep my upper body against it to counter any waver.

Thanks for the thoughts.

The best sounding one I've heard is the Electro Harmonix POG and HOG. Look into those. I use the Digitech Whammy and it's quite digital but it still gets the job done.

My personal favorite is the EBS Octabass. It doesn't sound natural either, but I like the way it sounds!