I think there is an "all of the above" approach needed (meaning some of the ideas in the thread, not the options in the article). Unique merchandise absolutely -- maybe can't do it in every category but in more than you think. Clothing and home goods and décor for sure, hardware, personal items like lotions, etc.
The combination of not finding the exact item on Amazon and instant gratification is powerful. Creating special deals of bundled items (a free or half price belt to go with that outfit). Offering a free service like installation at a certain purchase level. Directly addressing people who you know are showrooming by either meeting the Amazon price or offering a bundle price on the spot (not advertising this, but offering it only on an individual basis), making customer service so good that people really would feel guilty showrooming.
From every bit of research I've read, showrooming isn't as big a problem as it seems/feels. Yes people do it, but more people are researching online then going in-store to see and feel the item. If the price is within striking distance of Amazon the instant gratification and above and beyond service and experience will win out. And the good news is that Gen Z actual prefers going to brick and mortar to ordering online. At least in their current lifestage. So cultivating them isn't a bad idea either.