Climate finder: U.S. places of 50,000+ by their NOAA 1991-2020 normals
Set the limits you want; the finder lists the 459 places of 50,000 or more people that meet all of them, the ones with the most mild days first.
Source: NOAA NCEI 1991-2020 normals. Mild days: days a year with a normal high of 60-79°F.