Grizedale in the Lakes is good – quite rocky so depends if that’s ok with your wife. All sorts of riding to be had, gentle xc loops (like NF trail), steeper technical stuff, some killer hills.
Cheviots as mentioned above, unpopulated, nice days out with lovely views. The stuff that I’ve done was not as technical as the Lakes (Alwinton/ Barrowburn). Quite a bit of sustained climbing but nothing too steep, if that makes sense. Possibly consider some cheeky trails here to join up BW as you hardly see a soul.
Dalby is quite different to the above but has North York Moors close by to mix in some natural riding. Great Bear Active is a B&B in Pickering that do guided rides, skills etc. Stayed with them once and they were good. Never ridden the Moors. Dalby red was good for a day out.
Ridden around Malham in York Dales quite a while back and that was pretty. The rest of the Dales is unexplored for me.
If I had to choose I would probably go for the Lakes as there is so much riding close to where you stay. Tend to go out of season so can’t comment on how busy it gets. Have a holiday in Northumberland each year as my folks are up here and always enjoy it so that would be my second choice with rides out of Wooler, Alwinton and further afield Kielder. Did notice a lot of midge at Kielder last year and pleased not to camp.