The area around the cathedral in Amiens can indeed be called "charming", with lots of restaurants (but I have no specific recommendations) - more so than in Beauvais in my opinion. But there is not enough to do/see to spend 2 nights there. So I would either do a day trip in the area from Amiens, or spend one night there and one night in Lille. (Given that you would like to relax, I'd personally choose the first option: 2 nights in Amiens.)