  We have developed and tested a new way of coupling bolometric light detectors
to scintillating crystal bolometers based upon simply resting the light
detector on the crystal surface, held in position only by gravity. This
straightforward mounting results in three important improvements: (1) it
decreases the amount of non-active materials needed to assemble the detector,
(2) it substantially increases the light collection efficiency by minimizing
the light losses induced by the mounting structure, and (3) it enhances the
thermal signal induced in the light detector thanks to the extremely weak
thermal link to the thermal bath. We tested this new technique with a 16 cm$^2$
Ge light detector with thermistor readout sitting on the surface of a large
TeO$_2$ bolometer. The light collection efficiency was increased by greater
than 50\% compared to previously tested alternative mountings. We obtained a
baseline energy resolution on the light detector of 20~eV RMS that, together
with increased light collection, enabled us to obtain the best $\alpha$ vs
$\beta/\gamma$ discrimination ever obtained with massive TeO$_2$ crystals. At
the same time we achieved rise and decay times of 0.8 and 1.6 ms, respectively.
This superb performance meets all of the requirements for the CUPID (CUORE
Upgrade with Particle IDentification) experiment, which is a 1-ton
scintillating bolometer follow up to CUORE.
