If Saigon's heat overwhelms you, fly to Da Lat (1 hr) for cool mountain air or Sapa (via Hanoi) for rice terraces.
Da Lat averages 15–25°C year-round. Sapa is 8–20°C with mist and rain.
Both are 2–4 day trips. Book through Vietravel, Klook, or Sinh Tourist for reliable packages.