Recent interest in bistable devices for vibration energy harvesting has given evidence of their beneficial performance in realistic stochastic or low frequency excitation environments since the snap through effect (high displacement switching from one stable state to another) is a non-resonant dynamic. It has yet to be rigorously determined how adding additional degrees-of-freedom may influence bistable energy harvesting response since the nonlinearities do not allow for a direct analogy from multi-body linear examples. We analytically and experimentally assess the potential for improving energy harvesting dynamics by adding a conventional linear oscillator to a bistable energy harvester. The traditional coupling parameters of mass ratio and tuning ratio are evaluated as means to tune the harvester's response. Advantageous design regimes are classified and explanations for the rich dynamics are provided. Experiments confirm the benefit of appending a linear oscillator to the bistable system as a simple means by which to enhance harvesting performance.