LTC3531-3.3 - Mouser Product page is at
Buck-boost, 1.8V to 5.5V in, 3.3V out up to 200mA (200mA only with Vin > 3V) Will work with LiIon, Alkaline, and NiMH batteries.
ThinSOT23-6. Almost anyone can solder.
Three external parts - 10uH inductor, 10uF or more output cap, 2.2uF or more input cap.
Pretty good efficiency. Works well at very low load currents. Good transient response for intermittent high current loads.
Easy to lay out for DIY board creators.
Cost for IC is $5.04 USD from Mouser. A bit expensive! Available from DigiKey, Mouser, and others.
Given everything it does, I am not too dismayed by the price. If you just have to have one on a breakout board, I will have one or two extras by about March 1, 2020. PCB will fit on a standard spring proto board. Contact me via PM if you want info. Board layout is also available free on OSH Park (boards cost, of course, but less that $1 USD per board); contact me via PM for info about board layout & BOM.