Do what SuziQ and SirKit are doing ... radiant heat pads under the tiles, at least those in the bathrooms.
Ooooo ... toasty warm floors!
Yeah, we're doing Warm Tiles, which is an electric grid heating system. We're not doing the entire house, so the electric bill won't be affected TOO much. We'll be putting it under the tiles in our Master Bath, up on the third floor in the Teen Suite bath and down in the basement in the small bathroom there. It will be most important there, because there will not be a heating vent in there.
You can set the thermostat to go off at night and come back on a hour or so before you get up, just in time to get the entire thermal mass of the floor warmed. That way you're not paying to heat the floor all night. And you can do the same while you're at work. You only pay for the time you really need it.