Vijaypat Singhania holds the world record for [highest flight by a hot air balloon][1]. It was 21km (~69000 feet). It is eleven times more than what you need.

More information about the balloon he used can be found [here][2].


  [1]: https://www.guinnessworldrecords.com/world-records/highest-flight-by-a-hot-air-balloon
  [2]: https://mi70k.com/update4.htm