I would go for nant peris campsite (or other options in the valley ) then can just walk into the pass where you will find quality classic bouldering at all grades
No worries, if you've not been befor look for problems such as boysons groove, king of drunks, eutopia block, lordy lordy, etc, plenty to go at and eutopia block has some great easier problems to,
Llyn gwynant is ok but can get really midgy at times but handy for elephantitus cave bouldering. If you have transport then there are lots if campsites you could choose depending on what kind of site you want. Beddgelert forest has a large site with all the things you would expect from a caravan club but also takes tents where as the nant peris site is more cheap and cheerful with basic facilities but conveniently close to the pass for the bouldering, willies barn near tryfan is also good and I think there is a camping barn there as well if you prefer that. The campsite on the main road near capel curig is always busy, basic facilities but close to aa good pub and café which does good breakfasts, can't remember the name of the site but it's on the left as you go from Betws y Coed to capel curig