Custom Terrain Textures

Hello. I'm building a little prototype of a strategy game and from the beginning I want to create a 'map editor' so to speak. I'm using a plane, generated in code and then I manipulate the vertixes to create hills and such.

Eventually, I will need a way to create different 'biomes' so to speak, more grassy planes, rockier mountains or sandy deserts. Say in my data, I could assign each vertex to be of a certain biome (and using the 'map editor' I could paint these biomes on top of the mesh), but now I need a way to actually display these changes.

What I was thinking about, was using a custom shader, which would read the data about the biomes and display the right textures accordingly. Sadly, I have barely dabbled in the shader department, so I was wondering, maybe there's a different way to do this, that does not use Unity's built in terrain system? And if I was to use the shader route, how would I go about writing the shader? What information would I need to pass the shader, for it to work?