Heated Floor
I decided on ThermoSoft resistance heat pads, one in front of the toilet and sink, and one in the shower. They needed to be buried in the floor, so I raised the floor around the pads using 3/4" plywood. Total cost of pads, thermostat and sensors: about $600.
With the plywood in place, I could start covering up the pads.
For the shower floor, I first needed to float the right slope, while leaving enough margin to cover the heating pad.
I initially installed the thermostat too close to the shower. The village inspector pointed out during the rough inspecction that it wouldn't have passed electrical inspection, so I had to move it.
This is a better location, where the jacuzzi's pump timer was. Now I know why they put it way over there!
The black lines are the power, and the lines inside the clear tubing are the thermometers. The thermostat only uses one sensor, but a spare sensor runs under the shower in case the other one fails.
The instructions specify to put the power and sensor lines in separate conduit.