When to get a parachute?

I will be starting glider flying lessons this year once the weather warms up sufficiently, and am wondering at what point I should consider getting a parachute. I also plan to get my own glider, hopefully sooner than later, but will obviously need to be a certified glider pilot before that happens. I'm a fairly tall guy, so when shopping for a glider, I expect I will need to "try a few on". I plan to fly my own ship with a parachute, so that will be important to wear one when I sit in the cockpit. So the question comes up if and when I will need my own parachute. Maybe I'm jumping the gun here with this question? Thanks.