The SPICE and HeRALD experiments aim to probe dark matter (DM) masses at the MeV masses via nuclear recoils. This sensitivity motivates R&D which is now pushing the recoil energy threshold of Transition Edge Sensors (TESs) into the meV regime before then applying these next-generation phonon sensors to a set of well-motivated target materials. The superfluid 4He target (HeRALD) will benefit from both a low-mass target nucleus and a unique quantum evaporation phonon readout method. The complementary SPICE effort employs polar crystal target materials, motivated by their low-momentum phonon states and strong coupling to dark photon couplings.