Apply material to mesh based on height

Question

I have a randomly generated mesh with height from 0 to 20 and size of 100 by 100 And I want to do following to it.

If mesh height is from 0 to 7 apply material 1
If mesh height is from 5 to 15 apply material 2
If mesh height is from 13 to 20 apply material 3;

This problem has two parts:

1. Applying material based on height of mesh.
2. Blending material between heights 5 to 7 and 13 to 15.

I managed to achieve this in SRP by using a shader and textures instead of materials and using single material, however I am not a huge fan of it. Not to mention it doesn't work if I try to move to URP which is my goal.

Can someone suggest any resources how to apply material to mesh based on height? I have tired just doing meshRenderer.material = material; and that works, but it only applies one material. When I try to use all 3 materials by doing meshRenderer.materials = materials; it just seems to have some garbage generated, not to mention it is not height specific.

How can I achieve what I described above? Where can I learn more about materials, urp, and how to apply multiple materials to mesh and blend them?