I second Cambria and Morro Bay. There is a state park in the area although I haven't camped there.
I would look at Kings Canyon as well although you say you have reservations for Sequoia already. The drive to Grant's Grove in Kings Canyon is much easier than the road up to Sequoia. The road to Sequoia is as bad as places on Pacific Coast Highway and the traffic is atrocious but at least you are going slower. From Grant's Grove, you can drive to General Sherman in about 30-45 minutes depending on traffic and plenty big sequoias in Grant's Grove itself.