You can select a temperature that is comfortable for your body but this is not a prerequisite for meditation. Blankets are good, too, in some cases. Do what works for you but don’t get attached to it.

Meditation is about embracing all of life. If you get attached to a certain temperature, and keep yourself closed to other experiences, then your growth will stop. So, it can be said that there are optimum temperatures for feeling physically comfortable during meditation and this comfort zone may change from person to person, but there is no optimum temperature for meditation.