Best deal I've found. 100 top loaders, and a free gift of 100 penny sleeves. Ultra pro is the way to go!
Ultra Pro 3" X 4" Regular Toploader https://www.amazon.com/dp/B002K2MNGK/ref=cm_sw_r_apan_glt_fabc_YEGZHQM47DBXAHPAR82N?_encoding=UTF8&psc=1
I've not sent amiibo cards out, but I did sell a lot of Magic the Gathering cards in the past, if you're really worried about the cards getting damaged, you can pick up a pack of toploaders, they're hard plastic sleeves that you place cards into, after that, the standard bubble wrap or bubbled envelope fairs perfectly.
i did that and found they moved too much. I wish I had just printed them on normal stock and put them in top loaders, instead of having them print on card stock and then putting them in top loaders.
ultra pr plastic card sleeve + ultra pro trading card toploader for the win. all the benefits of lamination and yet it's easily removed for usage
(links provided to see what i'm talking about.)