If you want a dressy one at some point, the usual suspects are Smith, Brigg and Fox. I have a Smith myself, their one-piece/solid-stick version. The extra good thing about them is their shop is wonderful to browse, and they'll also cut the brolly to your specific height for no extra charge (important for a shorter fellow like me!)
Shipping to North America for brollies is unreasonably expensive though (due to the odd dimensions) so I'd wait until you're next in the UK before getting one unless you can find a US/Canada supplier, and then carefully check it onto your flight back. Talarico is an Italian maker well-known for their quality umbrellas, if you happen to be in Italy before the UK.
Well, as it happens, I plan to be in the UK in August, on a research trip. And even in Oxford, at some point, for when the University Press launches my book. So now that I know what to look for, I will definitely do some umbrella-shopping. Thanks!
(Once I've got the essentials covered, though, I really must give some thought to carvings and unusual materials, as you say. Do they make sword-umbrellas?
ETA, after web search: Holy shit, they do!