Rob, you've had lots of good advice already. Since we know you like good quality European and British firearms, and used, and like doubles, we've narrowed things down a bit. And having competed with you on a few auctions, I know we like similar rifles anyway. So here's some upland game shotguns that I like and recommend.
Try to determine if you would be happy with a 12 gauge. Good used ones are much more available than smaller gauges, ammo is universally available too in loads as light or as heavy as one could want. The 12 ga. guns are just a bit more bulky and heavy than necessary or desirable in the uplands. I personally find most British guns overpriced for our market. It's like the market for pre-64 Winchesters. OK, but, lots of other guys like them and drive up the price and they're not really that special.
If you don't mind ordering ammunition by the flat, a 16 gauge is well worth consideration. It is the "queen of the uplands" when chambered in properly proportioned small frame double guns. High quality used European 16 ga guns are more commonly offered for sale than one might think, because the gauge is seen somewhat as an anachronism now.
I shoot three 16 ga guns currently, my favourite is a beautiful classic double built by an unknown Italian craftsman with German steel barrels, double triggers and hammers. Just 6 lbs and very lively and deadly in the uplands. I think you'd like it.

I also shoot a Browning Citori White Lightning. ( tough, strong, steel shot capable, and built on a 20 ga frame) which has been my reliable go-to gun for a few decades. They're still made new.

And I shoot a very well made and artistic Merkel 211E/251E. The Merkel might just be the sort of gun you'd like - Well made, proportioned properly, lively handling, double triggers, and sometimes can be found like mine with a second set of barrels in 16/7x57R so that you can exercise your rifle shooting enthusiasms and shoot larger game with the same gun. There are a couple of these two barrel sets for sale in Canada at the moment.

You'd need to get the chokes on older doubles opened up by a competent gunsmith. That would add a hundred $ or two to the purchase price but is necessary and worth it - since nearly all those old doubles were choked very tightly and full chokes are unsuitable for quick shots at grouse in the alder thickets.
The most practical new gun choice is of course a 20 gauge. Lots of choices in maker and model, versatile, upland bird capable, and ammo is readily available. There is a silly fashion trend in new guns that promotes very short barrels. Please avoid that temptation. You'd be sacrificing shoot ability for "handiness" . No good wingshot would be found in the uplands with a double gun that has barrels shorter than 26", and even 30" barrels are no handicap. There is a good reason 28" barrels have been the standard length for upland bird double guns for generations. They serve the purpose well.