Thank you all for your comments, I really appreciate your feedback you've given me so far. I see that I probably should explane why balloon never falls down. It's because gravity is scaled by weight and I didn't add any addintional weight to balloon so that is reason why balloon is not falling when you don't have anything in your inventory.
@finn-truman I like your idea. Even my friends told to me to add this feature. After some testing I can say that this feature would improve balloon control.
@quasar47 I agree with you about the hitbox, it is quite hard to pick up something. But you're not right about spacebar spamming. You can only go up if you have some "jumps". Jump recovers every second, that is quite fast, but it's not enough to get you up when you have lot of things in your inventory.