I used 3 walls and 40% infill to make it more sturdy, but you can probably get away with 20% infill. 0.2mm layer hight, any PLA. Use PETG if you need to move the lamp a lot.

The picture of the wall mount is version 1 where I forgot the cable had to get in there, hence I made a version 2 with a gap for the cable so I didn't have to take the switch apart.

Did a few revisions on it and version 5 is now the one to use. Please note that the nut has to go on the side with room for it on version 5.