My approach to wild camping in England is 'what the eye don't see, the heart don't grieve over' - if no-one knows you're there, and no-one will ever know you were there, how can anyone mind? Pitch late and leave early, or pitch in a truly out-of-the-way corner and leave no trace of your presence, and you'll be fine. In the worst instance where someone does find you, and objects, you can pack up and leave, offer to pay the going rate, and no harm is done.
Having said all that, finding a spot that's both good to camp on and discreet can be difficult or can take up a lot of time. And wild camping spots rarely come with showers or a tap or an electricity supply. So occasional campsites are useful. Try joining the
Camping and Caravanning Club - they have a network of 'certified locations' - often gardens and farm fields - where five members at a time can camp. Sometimes all you get is a patch of grass and access to a tap; sometimes it's the back garden of a pub, sometimes it's part of a larger, commercial campsite. But being a member may get you access to certified locations in areas where there are few or no commercial sites. (The CCC don't shout much about those certified locations. They make their money from their much posher club sites).
It's worth being brass-necked about it too. If you see a spot where you'd like to camp, or if you're getting desperate, ask! Call at pubs and shops, knock on doors and ask if you can camp in a garden or borrow a corner of a field. Often you'll not only get what you wanted, you'll be invited for dinner/breakfast/a pint/all three. The worst that can happen is a blank look or a '**** off mate'.
Have to agree about hostels - they always seem to have those special dampers on the doors which, rather than closing them gently (as I thought dampers were meant to) actually make them bang closed more violently than ever.
Consider joining
WarmShowers, although I seem to recall there aren't that many hosts up the east coast (I know there's at least one, though, and that might fill a gap for you).
Finally, I know it's close to the Whitby end of your blank stretch, but there's
Beacon Farm just south of Whitby (important info: it's on the top of a hill - the clue is in the name...)