The usual French word for “bed” is le lit. There are however some slang synonyms. One of them is le plumard. It is derived from plume, which means “feather”.
J’ai passé la matinée au plumard.
I spent the whole morning in bed.
Another word is le pieu (which also happens to mean “post” or “stake”, but these meanings are unrelated).
J’aurais mieux fait de rester au pieu aujourd’hui.
I should have stayed in bed today.
A related verb is se pieuter: “to go to sleep”.
Je suis crevé, je vais me pieuter.
I’m exhausted, I’m going to bed.
Listen to the examples: