Motivated by the potential for cuprate-like superconductivity in monolayer rare-earth nickelate superlattices, we study the effects of crystal field splitting, lattice distortions and strain on the charge, magnetic, and orbital order in undoped two-dimensional (2D) nickelate monolayers RNiO3. We use a two-band Hubbard model to describe the low-energy electron states, with correlations controlled by a effective Hubbard U and Hund's J. The electrons are coupled to the octahedral breathing-mode lattice distortions. Treating the lattice semiclassically, we apply the Hartree-Fock approximation to obtain the phase diagram for the ground-state as a function of the various parameters. We find that the 2D confinement leads to strong preference for the planar d x 2 −y 2 orbital even in the absence of a crystal-field splitting. The d x 2 −y 2 polarization is enhanced by adding a crystal field splitting, whereas coupling to breathing-mode lattice distortions weakens it. However, the former effect is stronger, leading to d x 2 −y 2 orbital and antiferromagnetic (AFM) order at reasonable values of U, J and thus to the possibility to realize cuprate-like superconductivity in this 2D material upon doping. We also find that the application of tensile strain enhances the cuprate-like phase and phases with orbital polarization in general, by reducing the t2/t1 ratio of next-nearest to nearest neighbour hopping. On the contrary, systems with compressive stress have an increased hopping ratio and consequently show a preference for ferromagnetic (FM) phases, including, unexpectedly, the out-of-plane d 3z 2 −r 2 FM phase.