Dynamic DNS
Althiugh on further investigation it requires google etc to sign up. And the one we have looks more attractive now than it did!
Noip.com
The download and instructions for the client are here: https://my.noip.com/dynamic-dns/duc
satoshihost.ddns.net
3h4pc79scz2xcvi6.myfritz.net also works but only due to the router I have. ddns will work for anyone.
Could also Choose dynu.com which has a chrome plugin.
duckdns is also a free service.
and so is desec.io (also provides managed DNS)
https://www.dynu.com/
https://www.youtube.com/watch?v=wCJjiHp0d0w use that
https://www.youtube.com/watch?v=ZKEGP_qBmxg and this to fill the gaps.
https://www.dynu.com/DynamicDNS/IPUpdateClient/RaspberryPi-Dynamic-DNS specific to pi
https://www.dynu.com/DynamicDNS/IPUpdateClient/Chrome-Extension