My goal was to get a fanless setup (for a quiet office).

If that's not a requirement just get the Raiden Digit Light One, which does have a fan (and otherwise the same network card).

If I could design an adapter PCB myself, I would go straight to OCP 3.0, which allows for a much simpler construction, and TB5 speeds.

Alternatively, there are DELL CX422A rNDC cards (R887V) that appear to have an OCP 2.0 connector but a better heatsink design.