If there is natural gas outside your door, then I would definitely change over to gas. It is cheaper in a number of ways.
To compare you need to look at the cost per kwh delivered.
Natural gas is approx 6.5cent/kwh whilst kerosene is approx 9.0cent/kwh.
Next look at the cost of the boiler. A gas boiler is much cheaper than an oil boiler.
Then look at modulation. A 26kw oil boiler gives 26kw when on and zero when off. There is no in between, therefore, when the system is hot and say the demand is only 12kw, the boiler will still send 26kw and put the boiler into short cycling mode or if the hw circuit is the only circuit open, equally the boiler will short cycle.
Modern better quality gas boilers modulate in that they monitor the return temperature and turn down the output of the boiler to match the demand, so therefore only use the amount of gas required to heat that demand at that particular moment.
Final plus is no large bill as you are only paying for the energy you use and your gas can't be stolen.
Downside is the heating system must be clean so a powerflush is a must. Then put a high quality inhibitor to restrict sludge build up in the future. Gas boiler heat exchangers can be very restrictive and clog up easily. You should always have a pressurized sealed system with a gas boiler, therefore no solid fuel systems.
The final downside to gas boilers can be parts are much more expensive than oil boilers and boiler selection needs careful consideration, i.e. reliability, availability of parts, cost of parts, etc.
Obviously, whilst changing over, I would certainly zone the heating system with time and temperature control and boiler interlock and youcan avail of an SEAI grant at the same time.