I can personally recommend Castlerigg Campsite. I have stayed there before and my friend goes at least twice a year. The staff are very helpful with a good shop onsite. There is also an area just for the campers with sofa's and tables and you can use the cooking facilities, microwave and hob i think (at extra cost). Plenty of electric points to recharge any media devices and you get free wifi with a good range, if required. The toilets and showers are very well maintained and cleaned regularly and have heated floors if it gets a bit chilly, no extra cost for showers, oh and very hot! There is also a small farm with a few animals if you have young ones.
The only down side of it I found was the location, as nothing else near the campsite apart from a dodgy looking pub. Most days I drove 10mins or so to my walking start point ie for Catbells and Skiddaw but all depends what walks you are planning.
Overall, highly recommend Castlerigg Campsite, check their website and yes you can book in advance with them.