A small amount, on my wrists and arms, lasts quite a long time.
If I want more of an enveloping effect, I dab on a bit on both of my ear lobes (I learned this from Roja Dove).
As a Guerlain fan, you owe it to yourself to acquire some vintage Mitsouko extrait or Habit Rouge extrait. Or Vol de Nuit extrait. Oh hell...just try whichever one you can!