We have to remember here is that all electricity have the emissions of marginal electricity. So, if there's only a single gas-fired power plant running, that's the last plant profitable as electricity price rises and the first plant unprofitable as electricity price falls. Thus, if you can reduce your electricity consumption, that's the plant that will reduce its output as a response to you reducing your electricity use.
I assume that at least on non-windy hours, there will be gas-fired power plants running providing marginal electricity. However, due to the massive installation of wind power, if it's very windy the gas-fired plants may be turned off.
Therefore, I claim that most of the time electricity has the emissions of gas-fired generation. Gas-fired generation have an efficiency of 50% (actually it's slightly over 50% in state of the art, but there will be transmission losses so let's say 50%), as opposed to your gas boiler having an efficiency of 90%. Therefore, it makes sense to use the gas boiler.
If you are only concerned about emissions, you need some way to see if the marginal electricity is provided by gas-fired plants or by wind. If marginal electricity is provided by gas-fired plants, then electricity spot price will be about twice the cost of gas per megawatt hour (because of 50% efficiency). If marginal electrictiy is provided by wind, then electricity spot price will be whatever the cheapest load that can be increased on demand is willing to pay. In most cases, this will be some factory or a bitcoin mining operation. There may be some online service that tells the momentary generation mix. The key to look as is whether a single gas fired power plant is on. If even a single gas-fired power plant is running, that's the plant that will reduce its emissions as a response to you reducing your consumption.
However, there are several things to note. Firstly, as more and more wind power will be installed, there will be less and less hours when marginal electricity is produced by gas. Secondly, in the future gas-fired plants may capture the carbon dioxide, but I'm sure your gas boiler won't capture its emissions ever. Thirdly, more transfer capacity from Norway may be installed, and this may allow using Norwegian hydropower as the marginal electricity production method. Thus, my assumption is that over time marginal electricity will become cleaner.
Also, as you correctly noted, with electricity it's easier to fine-tune the heating of individual rooms.
So, I propose that you should make the decision on total cost. If the total cost of burning gas (and any maintenance the gas boiler might need) is greater than the total cost of providing resistance heat, use electric resistance heaters. If electricity is more expensive, use gas. In most cases, this will result not only in the cheapest heating, but also in the most environmentally friendly heating. Also you can consider in this comparison the costs of heating only needed rooms with electric resistance heat and the costs of heating the whole house with a gas boiler.
Also do consider split air source heat pumps that convert outdoor air heat into a higher temperature. They have a high installation cost but the investment may be useful as it reduces electricity consumption of heating to one third of resistance heating consumption. They also allow fine-tuning heating of individual rooms if you install a heat pump in every room, but of course a heat pump in every room will cost a lot.
Air-to-water heat pumps and ground source heat pumps may be an option too, but their investment cost is higher and in some cases it may be non-permitted to drill a geothermal well if there are underground constructions or plants to do such construction, or if the geothermal well could contaminate water supply.
With heat pumps, almost always electricity wins over operating the gas boiler.