I found a really nice way to do this. Especially since many links from deals sites etc will have their referrals going to them instead.
What I do, is create a bookmark on my toolbar to smile.amazon.com.
https://smile.amazon.com/gp/cart/view.html/ref=nav_cart
I load up my cart from any amazon links from external sites, but click that link to get to my cart. Then I know my donation goes to LMN instead of the referring links.