caves the title says it all

This mod is just a direct port of the old mod made by Simcra. I've implemented caves in my new Surfaces mod (https://mods.factorio.com/mod/Surfaces_API).

You can install this mod to get started: https://mods.factorio.com/mod/Surfaces_Config_Caves

Or you can create your own configuration mod. Do note that cave generation is experimental and a bit hacky, because factorio isn't really designed for different terrain generation on different surfaces. As such, I'm not very actively maintaining these mods, but it should work. Also note that there is not backwards compatibility with Surfaces Reloaded.

do i need to start a new game with that mod as i cant find caves in my old save

Yes, there is no migration between these mods. You might be able to use both mods if you can wrap your head around having multiple dimensions of layers.