I have never done online currency exchange, as the lira is so good we thought we would buy ready for this years trips
Buying ANY currency in advance is a gamble, especially one as volatile as the Turkish lira.
Couple of things to bear in mind - firstly, its showing no signs of recovering against the major currencies right now and when it does recover, its unlikely to be an overnight process. Secondly, who knows what effect the upcoming referendum will have - depending on what happens between now and then, the lira may end up in real bother when the result is known.
You need to make up your own mind, I'm no financial expert - but at this moment in time, I wouldn't be committing any substantial amount of dosh to the lira.
JF