We need Better Fly for the game !

It's 2021 now and we really need some way to apply flying other than "greater jump".

I have a vague idea about that:
1. Everyone is flying at a level of 20 feets. Thus it can be achieved by simply add a buff to the charactor
2. Flying creature is immune to melee attack, unless it's from another flying creature
3. Flying creature if immune to difficult terrain and most ground effect( unless it can affect as high as 20 feets.
4. Flying creature moves the same way as "greater jump"

It's not beautiful but already much better than foolish "greater jump"
And it's workable!