*IN my bed is more correct in English. ON my bed means that you're sleeping on top of the blanket. IN bed means that you are under the blanket.
Agreed: "in my bed" sounds much more natural to these American ears. That variation is also accepted now, but I would suggest changing that to be the default translation, not the alternative.
I was very pleased that "I want to sleep in my bed tonight" was given correct. For once, common sense prevailed.
The problem is that it could be translated in two ways in English. "Na" (em + a) can mean "on" or "in" in English. Native Portuguese don't distinguish the difference, unless they use something like "em cima da cama" for "on top of the bed."
I was referring to the fact that "tonight" was allowed. I get the in/on thing.