Actually it's much healthier apparently. Unfortunately it's a 1000000 times less comfortable so we are cursed to use comfortable beds for all eternity.
Полу is the locative case of the noun пол. Пол along with some other nouns (e.g. лес - лесу, берег - берегу, ...) has an irregular locative case. As far as I know there is no rule to help memorise this, you have to learn the exceptions.
It's wrong in this context (and means "on the field"). You would probably be understood, but it's wrong.
"спать на поле" = "to sleep in a field" =) Поэтому правильно только "спать на полу".
Ah man. I think I went about answering this the wrong way then, and got it correct by a-kind-of luck. I went with the whole "I" situation. Я любл"ю" ...... пол"у"
One of the correct answers that popped up was "I like to sleep on the storey." (Yes, storey.) Looks like a bit of confusion between "floor", what is under your feet, and "story", as in "second story." I submitted a report.
I answered "I love sleeping on the ground" and it was rejected; as an English speaker to me it means the same thing...
"Люблю" isn't only used to express feelings towards a living beings. It can (and often is) be used to express your enjoyment / pleasure in something inanimate or intangible - actions, objects. 'Люблю' is normally considered stronger than "нравится", but in certain contexts they're equal.
Yes, "мне нравится спать на полу" is a totally valid phrase and in this context I don't see a difference to using 'люблю'.