[snowman_al]

Personally I would expect the 2k headphones to be the best option and in reality little risk. Especially if you use batteries.
If you are bothered, you could use a very small 220v to 6-0-6 volt 250mA mains transformer as an output transformer. It would need low impedance (30 ohms-ish) headphones though, then you could try either a 6 volt or 12 volt tap for the loudest output. It would also isolate the set if you wanted to use an amplifier.