Are there constant voltage regulators regulating up and down for variable input?
The linear regulator won't do your work, like you say. Buck-boost is needed.

Sure you can boost up and then buck down. There are simple single-switch                      topologies that do this in one stage. Zeta, Ćuk, Sepic, or buckboost could work for you. The Ćuk and buckboost give a negative output voltage in their standard form. If this is no good then it narrows it down to Zeta or Sepic. Sepic has low-side drive which makes things simpler but at your low input voltage this is not too important.

There are lots of chips that will do this. These circuits are popular in omnivorous Leds.