I may be wrong, but I don’t think you’re going to find anything in-rack that’s smaller with 1/4" jacks. If you’re just trying to make all your 1/4" jacks mono, you’re probably looking for something like ADDAC Systems ADDAC200PI (pedal integrator). Or, if rack space is that tight, maybe go outboard and try either boredbrain’s INTRFX or Transmutron?
For my rig, I’m thinking of replacing my Bastl Hendrikson with a Knob Farm Ferry. The jacks are all 1/8", but the features seem worth it.