Flying Player

Hey, i would like to make a custom way for the player to fly, this is needed for my dragon ball mod, what i would like to do, is using a keybind with space bar and another key(F)
When the player press F, flying Mode variable is activated.(ez to do that) then, while flying mode is activated, when the player press space, the player with start flying like creative mode, ill do this by using movement vector thing... if the player in flying mode stop moving while flying, (sorry if that was not clear)so what im looking for now, is how to make the player like... stay in the air while in flying mode. because without that, when the player press space, he will just go up until he release the key and then he will fall.