My model before solidify:
Normals>Recalculate outside Mesh>Clean up>Merge by Distance Mesh>Clean up>delete loose Ctrl+s>Apply scale
Lower the thickness of the solidify modifier is not an option, sice The point of the modifier is to 3D print the body as a shell.
The only thing that works is to manually find the edges causing the weird shape, and move them manually. This is what I try to avoid, since it is time consuming. On the picture below I move the selected edges down on the z axis.