I have been buying these-->
https://www.amazon.ca/Wiper-Refills-ASLAM-Windshield-Wipers/dp/B082NWW9DM/ref=sr_1_1?keywords=Wiper+Blade+Refills+6mm+for+ASLAM+Type+G/M+Windshield+Wipers,+28"+Cut+to+Size(Set+of+4)&qid=1579924780&s=automotive&sr=1-1
They are 6mm inserts and fit the Model 3 wipers perfect. You get 4, enough to do the wipers twice for $19.99 cdn. They might will work on a Model S too. I like the idea I get to reuse the old wiper frame, they are cheaper, I keep the OEM wiper, no screwing with adapters and clips, etc. I have also bought the same for other vehicles from Canadian Tire. I don't know if they still carry them.
They are fairly easy to install.
View attachment 504016
Unclip the end. I use a couple very small flat head screw drivers to pry it off. Be careful not to break the clip.
View attachment 504017
After it is un-clipped the sleeve holding the metal rails can be slid off. Both sides are different so keep them sorted. After both clips and sleeves are removed the old insert can easily be removed and the new one put in. Then slide the sleeves on their respective sides and them put the clips back on.
I have done this twice now. I am very happy with the results. They work as new.