Hosting a minecraft server with sky broadband?

You should not need to re-do any port forward. The MC server should be set at a static LAN IP, one outside any DHCP pool range on the router. That way, the MC server is always at the same LAN IP. No need to change port forwarding, which is router to MC server only…
Now, as for the public IP address, if it changes a lot you can look into buying a dynamic DNS service, one where you buy a DNS/URL name and that site has tools to run on the MC server that checks and updates the DNS name to the current public IP (the one your ISP assigns to your service, and changes often…) Your friends then connect via the DNS name, not by IP address. Search the Internet for "dynamic DNS" or "dynamic name service".

It sounds like two separate problems.

First, if you are hosting a server on your private network, it should be on a static address on that network. The address must be in the same subnet as the private network, not used by anything else (router, subnet ID or broadcast) and it should be outside the range of addresses used by the DHCP service. You can then set up port forwarding to that static address.

Second, sign up to a DDNS service such as noip.com or dyn.com (there are others). Choose a suitable URL that your friends can use to access your server, and set up a DDNS updater. This might be a facility available in the router itself, or alternatively, the DDNS service will have a small updater program that you can download and install on your server machine. This will keep the URL pointing at your public IP address even if it changes.

Finally, if you are in the habit of turning off the router when you are not using it, stop doing it. Normally I would expect a public IP address not to change more than once or twice a week and possibly less frequently, providing the router is kept on.