I want the device to start as soon as possible, so a low input boost regulator is needed, but at high temperatures, the input voltage may get higher than 3.3V.  I need to see how well the adaptive thermal circuit works to see if we can keep the voltage below 3.3V, but for now I will plan on a buck-boost regulator that can start up with less than 1 volt, like the LTC3106.  That is probably overkill for this application and I may later try to replace it with an adaptation of the  joule thief and a linear regulator.