I have a 20 months old boy who needs warm milk at 2 am. Can anyone suggest what flask or Thormos I should Buy?

Can someone please suggest what product I should buy to keep the milk warm for 2 to 3 hours at night. I can come downstairs to use the microwave to heat the milk but that is too hectic, I don't want to use a burner..I would like to know if any flask or any other product I can buy