can anyone recommend and bivvy spots near the ridgeway, ox11 postcode?

I don’t know where OX11 is but there are lots of bivvy spots along the Ridgeway, just choose somewhere sensible.

I used to live there mate, East/West Hagbourne/Blewbury way. Problem you have for quietness there is the noise from the A34. Your best bet there is where people camp which is just up the top of Harwell, there’s a proper gravel area for parking just up from the A34, both sides of the main road up from West Ilsley on the map, you’ve also got one place about 1.2 miles back up the Ridgeway towards Harwell, that’s nicer too.