I grew up in that area…well…sort of grew up. Anyway… Some places to look up: Bacton Woods, Pretty Corner (Sherringham), Ringland Hills (Near Norwich but due to ‘trail building’, which was nothing less than sheer vandalism, mountain bikers were pretty unwelcome there last time I saw the area) and if you fancy going further afield…Thetford.
My two penne ‘orth is that North Norfolk is as hilly as Norfolk is ever going to get this side of the next ice age so the hills around you are as big as hills in that area are going to get. If I was in your position I’d take an XC bike and go exploring. What I used to do was take an OS map and try to string together as many of the ‘little bits’ of fun singletrack as I could find and just accept that you’d have to use tarmac or very boring tracks to join them all up again.