Yes, you do sleep on the floor. In Oume we placed a double pad on top of the tatami (compressed rice straw) floor. This was covered with a sheet and we slept between this and an under blanket with a futon light very fluffy blanket on top.
In Komatsu the arrangement was similar, but under the floor pads was a large electrically heated pad. The blankets on top of us are heavier than the ones in Oume. It is colder in Komatsu and the only room that is consistently kept warm during the daytime is the family room. This room is constantly being used.