If you have an amazon prime account you will get 1 year FREE of nintendo switch online
Twitch Prime | Nintendo
you get a 3 month freebie now, have to login with your nintendo switch account (does not have to be online-active already) and then in 60 days you can login back to that twitch page above and add another 9 months.
It turns on auto renewal so you will get billed in 3 months if you don't turn that off. Turn off auto renewal here
ec.nintendo.com
It does ask for a credit card (or paypal) when you sign up, I used a $0 balance visa gift card so nintendo can't fuck me over if I forget.