How can I use 2D sprites for characters in a game with 3D collision?

Hey all, I'm working on a 2D game with voxel(pixel?) terrain that is mesh/meshcollider based. I am pretty new to unity and programming in general and I can't figure out how to get the player/enemies to work. More specifically: I am having trouble assigning mesh colliders to an object with a complicated 2D sprite with animations. When I try to assign a mesh collider procedurally in script, nothing happens.

I don't need anyone to write my code for me, I am just looking for a general description of the steps I need to take to assign a mesh collider in script to an object with a sprite renderer component. Thank you for your time!