Combine meshes, Weld planes together

Hello! I need to combine meshes, but once I apply the texture, it must stay constant between meshes. So I'd like a way to easily merge quads meshes or draw a very complicated plane made of several rectangles that may or may not be contiguous.

I know of Mesh.CombineMeshes, but it won't create continuity between planes in UV mapping, and it would be nicer to just really have one big mesh.

Thanks.