It’s possible to have a hybrid system where your heat pump provides most of the heat you need but is backed up by your existing boiler, wood pellet, or log stove that you can turn on when needed.
This can give you experience of living with a heat pump but as you make insulation upgrades to your house the heat pump will provide more and more of the heat that you need, until it is eventually supplying it all. Making those insulation upgrades may also eliminate, or at least reduce, the need to upgrade your existing radiators.
This allows you to take a staged approach to retrofitting your home, and potentially to use the type of heating that is cheapest at the time. It can also be cheaper and simpler to install.