Since we're only dealing with one PC, how powerful is he for his level? Is your player very good at crunching the numbers? And how much magic equipment does he use? That'll probably determine what level of adventure you can send him on. Monks benefit greatly from pretty much all kinds of treasure so even with the basic stuff-bracers of armor, periapt of wisdom, gloves of dexterity, etc... he'll be able to get massive AC/saves after adventuring for only just a while. If you can, post the important bits of his stats here.