Yep the wildcard certificate. Although cost wise I hadn’t suggested this because of its price in the event you’re purchasing the ssl certs from a certification authority.
I used comodo in this quote
I mean look at that! 43k each year? Just for the certificate? You’re better of buying a separate hosting plan that offers a complimentary certificate.
With regards to the wildcard cert on Letsencrypt, last I checked(which was sometime early this year, so I might be outdated here) there were some complications and they postponed the API release.