  BINGO is a project aiming to set the grounds for large-scale bolometric
neutrinoless double-beta-decay experiments capable of investigating the
effective Majorana neutrino mass at a few meV level. It focuses on developing
innovative technologies (a detector assembly, cryogenic photodetectors and
active veto) to achieve a very low background index, of the order of $10^{-5}$
counts/(keV kg yr) in the region of interest. The BINGO demonstrator, called
MINI-BINGO, is designed to investigate the promising double-beta-decay isotopes
$^{100}$Mo and $^{130}$Te and it will be composed of Li$_2$MoO$_4$ and TeO$_2$
crystals coupled to bolometric light detectors and surrounded by a
Bi$_4$Ge$_3$O$_{12}$-based veto. This will allow us to reject a significant
background in bolometers caused by surface contamination from $\alpha$-active
radionuclides by means of light yield selection and to mitigate other sources
of background, such as surface contamination from $\beta$-active radionuclides,
external $\gamma$ radioactivity, and pile-up due to random coincidence of
background events. This paper describes an R\&D program towards the BINGO
goals, particularly focusing on the development of an innovative assembly
designed to reduce the passive materials within the line of sight of the
detectors, which is expected to be a dominant source of background in
next-generation bolometric experiments. We present the performance of two
prototype modules -- housing four cubic (4.5-cm side) Li$_2$MoO$_4$ crystals in
total -- operated in the Canfranc underground laboratory in Spain within a
facility developed for the CROSS double-beta-decay experiment.
