of good sleep

[blouen]

You need to get at least 4 hours for good sleep a day.

It should be:
You need to get at least 4 hours of good sleep a day.


Why

[Tina Michelle]

You are talking about what you need:
4 hours of good sleep

If you were talking about how much time to set aside for the purpose of sleeping, then you could say:
4 hours for good sleep

[Offroad]

please, is there a difference between "sleep tight" and "sleep well" ?

Many thanks

[Tina Michelle]

In my opinion, "sleep tight" is something you would say to a child or someone you are very close to, like a family member. "Sleep well" sounds a little more formal.