Have had both nubuck and leather Birks, and have found the leather ones hold up better over the long-term. The nubuck material tended to stretch and lose supportiveness over time. I think you made the right choice, definitely! I also agree about breaking them in before you have to wear them all the time - it can be hard on the feet for a few days there, and I'm sure you don't need that on top of hip surgery!
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