Shoppers with mature skin swear by the $7 Nivea Cocoa Butter Body Cream. It’s among Amazon’s best-selling body creams, and more than 20,000 people snagged it this month.

The skincare world has been buzzing with speculation about whether Nivea’s classic creme moisturizer — which costs just $10 — is a viable alternative to La Mer’s cult classic cream, which will set you ...