Current terrestrial gravitational-wave detectors operate at frequencies above 10Hz. There is strong astrophysical motivation to construct low-frequency gravitational-wave detectors capable of observing 10-1e4 mHz signals. However, there are numerous technological challenges. In particular, it is difficult to isolate test masses so that they are both seismically isolated and freely falling under the influence of gravity at mHz frequencies. We propose a Magnetically Assisted Gravitational-wave Pendulum Intorsion (MAGPI) suspension design for use in low-frequency gravitational-wave detectors. We construct a noise budget to determine the required specifications. In doing so, we identify what are likely to be a number of limiting noise sources for terrestrial mHz gravitational-wave suspension systems. We conclude that it may be possible to achieve the required seismic isolation and coupling to gravitational waves necessary for mHz detection, though, there are significant experimental challenges.