Might I recommend checking out Kalium strings. They sell individual strings or custom sets to keep balanced tensions for drop tunings. I've been using them for years on an old Ibby Roadstar (avatar pic) tuning A#, C#, G#, C#. I had to file the nut to accommodate that A#, but otherwise it keeps nice tension, nothing is floppy from being down tuned, and no tweaks were needed for the truss rod. If you go that route, you can just pick up whatever bass you like the other specs on best and not be concerned with multi scale or 35" scale 4 strings.
Best of luck!