Sleeping Beauty On The Floor

My 5 year old boy has the habit of sleeping on the floor. Around his bed-time hour when he feels sleepy, he lays on the floor and falls asleep almost immediately. I take him to bed, but a couple of hours later, he appears again sleeping on the floor, sometimes in his own bedroom, others in any other room of the house. I take him two or three times per night to his bed, but again he slids to the floor and I find him there almost every morning. I´ve tried putting a mattress on the floor, but he ignores it. The same with a carpet and a folded bed cover. He definitely prefers cold surfaces! He´s been doing this for almost three years. He says he does it because he is hot, but he has done it several times during winter, once even laying down on a glacial marble step. I guess my child is a little fakir!