Why are so many pointing you toward a Fox? Several reasons, though some here may not agree.
Foxes, A.H. Foxes that is, are very close to, if not the, simplest boxlock ever built. Less internal parts, those parts being made from excellent steel and properly hardened. Less parts to begin with, coupled with a nearly perfect mechanism means high reliability. I've been shooting them for many years and never had one to fail me.
Stock dimensions on Foxes seem to be a bit "better", according to what most modern-day shooters want, than many other classic brands. L. C. Smith, for example, is a fine double, but I have a heck of a time finding them, in the condition I like, without excessive drop at heel.
Thirdly, there never has been a more elegant design for a boxlock receiver built, IMO. The Sterlingworth, which was the lowest grade Fox built, has an unadorned beauty that no other boxlock can boast of. Many of the examples of graded Foxes are absolutely stunning.
Fourthly, the internal parts in a Sterlingworth are just as well made and fitted as those in a high grade Fox. And that does not mean that the graded ones were neglected inside, just that no shortcuts were taken on the inner workings of the lowest grade Fox.
Lastly, there a lots of 'em around. If you've never seen a A. H. Fox and shot one, you're in for a treat, and an eye-opening experience.
Well, that's a start.
Good luck, Stan