Don't worry about the distance
Don't both trying to calculate the distance to the Sun. The exact number of astronomical units has no qualitative effect on the world or story.
What I can tell you is that a suitable distance certainly exists. And I'll tell you how I know too.:
Put your planet too far away and it will not evaporate at all. Put it too close and it evaporates in ten minutes. Somewhere in between is a distance where it takes 10 billion years to evaporate fully.
Put your planet there.