You're worrying too much. Whatever temperature is OK for you will be fine for a beardie for a short time. If it's further - a cardboard box with a hot water bottle (covered) will be fine.
Beardies can cope with quite cold nights in the wild.
Draco dormiens nunquam titillandus
“... there is no shame in not knowing. The problem arises when irrational thought and attendant behavior fill the vacuum left by ignorance.”