I don't know why it took me so long to figure this out, but there's no real reason to have more than one HV board layout. You can simply stuff the SSR based components for a contactor or the MOSFET parts for the DC relay and leave the unused side unfinished.

I've also decided to go with a 10W AC-DC module, as the HV board is shared between this project and the Pi EVSE Hat, and in that version of the project it's also necessary to power a Raspberry Pi with the 5v power output. Powering a Raspberry Pi and a 12 VDC relay is probably asking too much of a 5W power supply.

I've got this design into OSHPark and will report on whether it's a win or not when those boards get back.