I am trying to model a violin belly and I am intrigued, how is it possible to make faces with soft / rounded edges?

The edges I do are totally straight (see the blue amoeba).

Also, do you have some idea on how to avoid the edge loops getting too "compressed" in the middle of the model (see the red amoeba) ?

[![Please look at the red and blue amoebas](https://i.stack.imgur.com/BEITj.png)](https://i.stack.imgur.com/BEITj.png)

I know the Subdivision surface modifier, but I want curved edges after applying the modifier like in this picture
[![enter image description here](https://i.stack.imgur.com/b0arG.png)](https://i.stack.imgur.com/b0arG.png)

In fact, I've tryied to model using nurbs and bezier curves, but I wasn't able to find any tool similar to loft that works with curves, then I was forced to convert it in meshes, the results were not terrific and I've started to move the vertices manually, a real pain...
Unlike a guitar, each edge loop is on a diferente elevation on z axis and I have to keep the original dimensions,
So I have to be extremely careful when using the subdivision suface modifier.
I've already modeled this think on three different CAD softwares, but the meshes are far from good.

I want to improve the edge loops, but it will be a long path.