Restoril, with alcohol. It's a benzo, whereas Zopiclone is not. Benzodiazepines and alcohol are both central nervous system depressants, which will potentially cause respiratory distress followed by arrest. I say alcohol because it's difficult to OD on benzos alone; I once had an ER physician tell me the only way to kill yourself with benzos is to occlude your airway with them.
Apparently, there have been rare cases of CTB with Zopiclone documented, but there's no mention of whether alcohol or other substances were involved.
So, I'd say Restoril + alcohol, but I have no idea what dose. I'd say why not take both drugs, just to be safe.