Swivel Base Needed

I'd think in terms of something round, as the square, hexagonal and triangular ones require a lot more torque.

I'd get something that only swivels 180° too. That way you can't twist the wires in two.

There's wires? What wasn't I told

Here is a rotary bracket for the top and bottom of your cabinet

... and here is a standard wall bracket.

These, and the many standard suspension parts are shown here

As a bonus, the connectors are hollow... this will allow cabling to run into the cabinet through the fixture... now that we know there is cabling.