What you can do is put the gravity to 0 while the player is holding the jump button until a set timer ends. So that you can control the time spent in the air and don't get any unfair jumps because of too much reaction time (lol)
Like : every frame add 1 to the timer and put gravity to 0 if jump is held than if the timer reaches 10 reset it and wait until the jump button is pressed again.
