Laptop adapter + DC buck/boost converter or buck convereter only?
A simple buck converter should be more than sufficient for your needs. You can try making one yourself with an MC34063 + external switching FET or an LM2596. Modules for both of those are available online as well.

A single buck converter will, in most cases, be more efficient than a buck/boost converter. The latter generally finds applications when you're drawing power from a battery, where the input voltage can vary over a range. Since you're using a laptop adapter, you can expect a steady supply voltage and use a buck converter.