I have a 3 bed house on LPG – but it is old (1850’s), solid walls (not insulated), bedrooms in eaves (minimal loft insulation), mostly double glazed – but still can feel draughty. I am in a rural part of central Scotland (maybe colder than where you are). I also have a combi boiler.
I pay £154 per month, but did pay £215 when there were others (and kids) in the house. I also have a couple of wood burners – but admit that I have the heating timed for 90 mins in the morning and 4 hours at night (the wood burners just supplement the evening heat, and keep me going during the day at weekends). The rest of the time it is on a base of 6c.
I am presently on a fixed tarif, you can shop around and get deals – but it isn’t as easy as it should be. If you change supplier the new supplier has to take on responsibility for the tank and pipes, this is fine in theory, but causes problems if the tank is old / badly placed etc.
I love the place that I live, and to live here LPG is the only option. If mains ever came out from the village I would of course grab it, but you just have to weigh up the benefits.