Best way to power a 3.3V circuit from 3.3V-to-5.0V source
Here's a method that uses a low-cost coupled inductor and meets your requirements. 



You can also look at Sepic and Cuk topologies. Here's a comparative study entitled "A COMPARATIVE STUDY OF SEPIC, CUK AND ZETA CONVERTERS", but I suspect your solution will be more of a shopping expedition for the best chip for this task. 

If your user can connect this to whatever random supplies they have lying about, you should consider reverse voltage and overvoltage protection as well as undervoltage lockout and thermal or overcurrent protection against brownout conditions.