Saw this post late, not directly related to your power switch need, but just in case : the Aeon Labs DSD37\US Range Extender works also on 220-240Vac, although it is not documented.
More generally, the issue for AC powered switches is that if you use a step down transformer (240->110Vac), the safe bet would be that your switched loads would likely have ALSO have to operate at this reduced 110Vac voltage…
…and the step-down transformer would have to be powerful enough to support ALSO the switched loads.
This could be an issue for heavy switched loads (electric heater, garage door, etc…).
Only checking very precisely how exactly works the Z-wave switch would tell you if OK with 240Vac for loads only, or not.
A solution to have the Z-wave switch operate at a stepped-down 110Vac voltage, while keeping the controlled outputs at 240Vac would be to use an intermediate power relay (electronic or mechanical) between the Z-wave switch and the power load, which accepts 110Vac (or less) as control signal and supports 240Vac loads.
But it is only practical if you have only ONE or two such switches, and you need some electronics fluency to set up the whole set.
BTW, the ZIPATO MICROMODULE SWITCH DOUBLE you mentioned earlier should work fine at 240V & 908MHz (PAN04-2).