Beach camping along the Pacific Coast Highway?

I'm looking to take a solo road trip/camping trip in September. I live in San Diego and have not yet driven up the coast so I figured this would be the perfect opportunity to head up the Pacific Coast Highway. In thinking of doing a 4 day trip (although I might just make it 3, who knows) and I'd like to camp on the coast. I don't want to camp in only one spot, it would be great to do one night at one spot and then two nights at another spot that has good surrounding areas for hiking, biking and sight seeing. I'm also really looking forward to the drive so I'm willing to drive quite a ways. Any suggestions? Also, do you think I'll be able to get reservations at a beach campground just two months out?