This is a concept known as a rockoon[0]. Unfortunately high altitude balloons become really big really quickly, and even if you were starting at orbital altitud

This is a concept known as a rockoon[0]. Unfortunately high altitude balloons become really big really quickly, and even if you were starting at orbital altitude you would still need a decent sized rocket to reach orbital velocity. [0] https://en.wikipedia.org/wiki/Rockoon https://en.wikipedia.org/wiki/Rockoon