Zeeman-Sisyphus deceleration (ZS, ZSD) is a method for slowing polar molecules while scattering only a small number of photons when compared with direct laser cooling. It also ensures that molecules are transversely confined by application of transverse magnetic field gradients. It has applications in ensuring that a wider range of molecules, including heavy molecules and those with otherwise unfavourable vibrational branching ratios, can be slowed and confined to within the acceptance of a magneto-optical trap. This work presents results on progress towards a demonstration of ZSD for a CaF molecular beam and towards development of a ZSD scheme for YbF. First, a helium buffer gas source for CaF is presented. The source produces a beam of CaF moving at \SI{159\pm1}{\metre\per\second} and with a molecular flux of \SI{2.6\pm0.1 e8}{\molecule\per\steradian\per\shot}. The beam is used to test a ZS decelerator designed for CaF and it is found that molecules are transmitted through the decelerator. A second source, using a neon buffer gas, is also presented. It is shown that the pumping speed of neon by cryogenic adsorptive charcoal pumps is \SI{3.4\pm0.5 e5}{\litre\per\second}. This is compared to \SI{1.22\pm0.06 e4}{\litre\per\second} measured for helium. The higher pumping speed means that the neon source can be run with higher flow rates whilst maintaining a lower chamber pressure, and hence a higher CaF mean free path. Secondly, a ZSD scheme for YbF is developed and simulations to investigate its dynamics are carried out. The scheme utilises solenoids as a way to increase the physical size of the central bore of the decelerator and makes use of a transverse optical pumping scheme to mitigate the effects of the complex energy level structure of YbF.