Storage heaters are only cost effective if you have a dual rate meter such as Economy 7 where you pay for all the electricity you use overnight at a cheaper rate.
As you have a smart meter it should be possible for the electricity company to charge you two different rates - the meter should give them enough information for them to know how much electricity you use overnight and during the day and charge you accordingly but finding a provider prepared to do that may not be easy. Many energy suppliers simply do not offer a two tier tariff anymore and if you already have a dual rate meter they charge you the same for day and night usage.
Sadly any electric heater is going to cost a lot to run but this article has a comparison of running costs for the different types
https://www.cse.org.uk/advice/advice-and-support/room-heaters
Halogen heaters are the cheapest to run but the one I had was rubbish. It only heated what was directly in front of it and not the room itself - so it seemed to me. Oil filled radiators are the second cheapest and that is what I would buy if I had no gas supply.