I Needed This Breather

At last, after some sizzling days (You could say "after some hot days" or "after some very hot days"), today we can breathe better (I would personally move "today" to the end of the sentence but that's just what I'd do). It has been possible to walk by street ("on the street" seems to work better for me in this context) in the morning and switch off the air conditioning unit. The house temperature has lowered and we will be able to sleep more comfortable (What you said is fine, you could also say "more comfortably" or "comfotably") at night. However, the weather prediction indicates that the heat will come back soon. It is normal in summer! (You could say "This is normal in the summer!") 

That must be a really bad heat wave. Good luck getting through that and keep up your English studies!