Our overarching goal is the development of wavefunction-based quantum chemistry methods that give good results for both weakly- and strongly-correlated systems, that preserve as many fundamental properties of the exact wavefunction as possible, and that are computationally affordable and black-box for the end user. Many of our contributions in this area are based on the archetypal quantum chemistry method, coupled-cluster theory, and they have resulted from our efforts to understand and remedy the failure of symmetry-adapted coupled-cluster theory in the presence of strong correlation. In this thesis, we recount these investigations and discuss the key insights and results that they have produced. We describe in detail the novel wavefunction approaches we have devised, as well as the approximations and considerations one must make in order to arrive at useful equations. We believe that this work could be important for the continued development of affordable methods capable of accurately describing a wide variety of quantum chemical systems.