I have a PC I have installed Portainer on, with various docker services (home assistant, jellyfin, etc..) with an ISP supplied router fixing various device IP addresses and reaching out to dyndns.
I really want to move everything over to HTTPS connections by supplying certificates, tls termination, etc .
The issue I have is self signed certificates mean I have to manage certificate deployment to everything in the house.
I figure I need to link a domain to the DynDNS entry and arrange certs for the domain. However I can't make the link function and everywhere wants >£100 to generate a certificate.
As far as the money, you could use DuckDNS. It's free with the certificate. Not wanting to expose your network, I'm not understanding why you would want to use https. You could use wireguard instead.