Everything that can be said, has been said. Get a TRMS multimeter if you want to make sure the current and voltage are absolutely within their operating values. They're only 50 euro these days. Alternatively, borrow one.

the Folham workhorse is an electronic ballast often claimed to drive small SOX lamps correctly and is a rapid start floro ballast so a starter is NOT required and is available in 220-240 volts 50 HZ
maybe put a saved search on EBAY till one comes up and like stated above check current / voltage once SOX is lit

I wasn't successful in my past attempts to run SOX18 off of F20 ballasts. It wouldn't warm up or get bright and I imagine F20 and F18 are similar enough. That's why I said I was much more successful in using a 2 lamp F32T8 ballast wired to one SOX with both blue wires and that was perfect looking.

The problems i mainly had with 120V F20 preheat choke ballasts included not having the lamp striking at all with FS2 starters and having buzzing and failing ignitors when attempting to ignite the lamps using ignitors designed for low voltage high pressure sodium lamps.

However, when I tried using 277V F20 preheat choke ballasts in conjunction with FS4 starters and a 120V to 277V step up transformer, my 18W SOX lamps managed to maintain a stable arc and operate as intended. However, some FS4 fluorescent starters would not work while others struck the lamps without any issues except for a very long blinkfest with some starters.

the Folham workhorse is an electronic ballast often claimed to drive small SOX lamps correctly and is a rapid start floro ballast so a starter is NOT required and is available in 220-240 volts 50 HZ
maybe put a saved search on EBAY till one comes up and like stated above check current / voltage once SOX is lit

Yup, I believe there's a universal voltage and frequency version of the Fullham workhorse ballasts that runs directly off the mains in *most* countries. I think Japan being one major exception.

there are "WH UNV" series that are 120-277 and they start with a "4" in there number with the WH41 being recommended for a F20T12 single tube
and they offer there "normal" series in 240V configuration and being electronic are 50-60 HZ compatible