Red Dwarfs
The red dwarfs that make up almost 70% of the stellar population of the Milky Way are notably dimmer and smaller than the sun. So, the habitable zones of these stars, the range of the orbital distance where liquid water could be steady on the surface of a world, lie way closer in than they are in sun-like systems.

Habitable-zone red dwarf planets are tidally locked, which is not a good thing for habitability, as it can leave the world with a fright nightside and a scorching dayside. But in the case of a thick atmosphere, the heat can be globally distributed and mitigate extreme temperatures.