A couple of different sizes are the best. One for smaller animals like mink, etc. And a larger one for cats and canines... depends on what you are planning to trap and catch the most. for your area I would start off with a 2x6
A 2X6 in the shape of a fox board, curved to fit your fleshing knife, will handle all pelts other than small critters mink, marten, rats and squirrels which are easily fleshed on their forming boards with a small pelt stirrup scraper.
When your fleshing with curved blade you should be holding the knife just about flat so there Is no need to curve your beam to match the curve of your knife. What about the knives with out a curve to the blade. All you need to do Is round off any square edges.