How do I shop for an efficient low-current buck-boost converter?
A regulated charge pump can be more efficient at low currents; check out the LTC3246:
https://www.analog.com/en/products/ltc3246.html
This type replaces the switching inductance with capacitance, which can make the overall circuit smaller and cheaper as well.  Ripple will probably vary by input voltage and input stability; at lower input voltages, it just functions as an LDO.