Yeah Hubbard & Hubbard that I recommended is a more approachable take on Calculus on Manifolds (which it is based on or inspired by). It's still not simple, but

Yeah Hubbard & Hubbard that I recommended is a more approachable take on Calculus on Manifolds (which it is based on or inspired by). It's still not simple, but it's probably a bit easier-going for the modern student than Spivak.