I've been using ZeroSSL for over 5 years and can attest that they are friendly in that I have literally never seen or heard from them.
I've set up and cancelled multiple domains in this time, and have had one domain running for the entirety of my time with ZeroSSL.
I don't think you (OP) are gonna find much better than a for-profit business with a good track record if you're unwilling to use Letsencrypt.