When I say the floor is comfier I mean it, no mattress or anything, and at most I use the support of a pillow or two. I live in an area where it’s consistently hot, where it really only drops below room temperature in the winter, so for a good majority of the year so falling asleep is difficult. The hot weather makes couches and blankets pick up heat too easily. Even if I lived in a cooler area I would still detest beds and couches since I tend to find soft surfaces to be rather unpleasant. On the other hand, the floor, which usually carpet, usually has a hard surface with a consistent temperature that makes it enjoyable to rest on. I like hard wood floors too since the cold feeling is nice I find to be pretty refreshing, but not in a thirsty kind of way if that makes sense.
I have a shikibuton and a very expensive mattress. I vastly prefer my shikibuton and sleeping on the floor. It tends to be cooler as you say, and my cat comes and lays right next to me sometimes rather than on me. Plus the floor is more supportive than the mattress without being overbearing.