Some registrars offer an API to their own (free) DNS service which makes it possible to update records automagically. An example of such is Gandi (https://gandi.net), which also happens to be the one you use (according to whois). This way you're free to do any sort of DNS trickery, including simple dynamic updates through a cron job on the router. Given that you already have a domain with them and use the Gandi name servers it should be easy to set up something to do just what you want. You'll need to get an API key first, for more info check http://www.gandi.net/domain/api

Have you tried Hurricane Electric DNS? https://dns.he.net

You can update your IP with curl!

I built a simple bash script that just needs curl for AWS Route53 updates, https://github.com/systemx-xx/route53-bash