An Procedural flying Island Creator

Hi everyone,
i want to make an proccedural floating Island Creator like the Picture. Have someone Ideas how i can make one?

I heard about Perlin Noise but i think it became not the Right Shape, and GAIA Pro from the Unity Assetstore cant make it too.

With that Problem i had a new too:
The World Generator must be Run good on an Intel i3 7th Gen(not for Unity Editor for the Game) too, where i can save useless things how eating my Performance with getting an huge huge World?

 

This is definitely well-travelled ground... start with some simple tutorials on Youtube.

 

°-° I think am dumb

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XD