Force www on WordPress Multisite

Hi!

I have a wordpress subfolder multisite with domain mapped subsites. Everything’s awesome and works fine, if not for the fact that all the subsites do not have the initial www in the url. What is the best way to force the www from https://site.com to https://www.site.com?

I’ve seen people use the MU domain mapping plugin on older WordPress versions, I’ve seen people modify the htaccess file on newer versions (but not in all cases it seemed to work), it’s just that there isn’t a clear guide on how to setup the WordPress Network, DNS records, and sync them with other tricks (such as htaccess and whatnot) in order to have everything clean and functional, avoiding redirection loops etc.

At the moment my network is on the main site’s server and all other domains point to the respective subfolder via DNS config, some have email on the domain and others on the server. All sites are HTTPS, we’re working in panel with add-on domains.

Any suggestions? Please le me know, thanks!
– Joseph