Your statements about earth being round, oxygen and temperature are correct. Indeed a man by himself can not travel in space without life support as of now according to established science.
The fact that Prophet (P.B.U.H) went on Miraj is in the following verse in Quran:
Exalted is He who took His Servant by night from al-Masjid al-Haram to al-Masjid al- Aqsa, whose surroundings We have blessed, to show him of Our signs. Indeed, He is the Hearing, the Seeing.
Here Allah (S.W.T) mentions that Prophet went on Miraj but not how he was taken there. We can not say something is wrong according to science unless we know how that something happened correct?
And we're missing a point here. Prophet (P.B.U.H) did not go on Miraj by himself. Allah (S.W.T) took him there. We are talking about creatorThe Creator of the universe here. He who has created the universe is not bound by the laws of physics that he has designed for us.
Certainly, Allah has power over all things.
He who can bring Adam (P.B.U.H) from Heaven to earth without space suit can very well take a man from earth and ascend him up to sky without life support.
If I write a computer program and restrict its behavior based on certain inputs it doesn't mean I can not modify it or add provisions in it to behave differently when I'm using it.
And Allah (S.W.T) knows best.