I buy underwear online from Mack Weldon. The only other clothing I’ll buy on line is directly from denim houses like J Brand, Raleigh Denim and Nordstrom, where I’ve already bought items at a local and very well-curated men’s store and am absolutely sure of the fit. I’ll buy Alden shoes and boots online since with them I know 10.5 will always fit perfectly. Suits, jackets and other apparel are always bought at favorite stores since I’m uber particular about fit.
I agree with others about the negative influence of Amazon on brick and mortar; however, I do buy a ton of non-clothing stuff from them. In the Seattle area, especially Anacortes, there are marvelous used and new bookstores which I support since they’re a treasure.