Do I actually need to do anything during the PSTN switch off?

Unfortunately doing nothing isn’t an option in the long run. At the very least, you should check whether any of your security, and telecare systems use the PSTN network. It also benefits you to check what competitive full fibre options are available to you in your area. Community Fibre offer full fibre broadband packages with the option to add Calls — all from just £24.50/month — by far more competitive than many national providers.