Home working heating one room suggestions

We've got a full evohome setup with 9 zoned rooms, but my WFH default is still a small, 650w oil-filled radiator tucked under the desk by my feet, with a thick blanket covering my legs to trap the heat in that area.

No figures to back it up, but my thought was running the GCH just for one room is less efficient and costlier than what I'm doing. However, when other rooms/zones have their programmed heat on (kitchen and family area before school) I've got the office zone 'on' then to give the room a boost. Room I work from is far less than ideal being north-facing with 1.5 external walls, high-ceiling stone-built mid-late1800s, but it's all I've got available to me.

Also thick slippers and wearing an extra fleece over my hoodie. Only my hands that occasionally struggle with.

Don't forget gas is a third the price of electricity. So heating one room to needs to be using not power to be cheaper than just heating the house with a gas boiler.

Using electricity for heat to whether it is a room, a kettle, or a tumble drier is hugely expensive compared to other uses.

Don’t forget gas is a third the price of electricity. So heating one room to needs to be using not power to be cheaper than just heating the house with a gas boiler.

I know, that's the bit I need to get figures for. Not entirely sure how I can work it out with any degree of accuracy to compare heating the one room for WFH with my 650w oil-filled versus GCH via evohome.

Separate point but just taken delivery of some fingerless gloves to help with the cold hands. I feel so old now.

Edit:

Electric heater @ 650w on a thermostat for 8rs/day (assuming it's 'on' 50% of the time due to thermostat) @ 33.76p/kWh = (0.65 x 4) x 33.76 = 87.78p. So call it 90p/day to heat my office via electric oil-filled radiator.

I just need to isolate a similar outside temp day to measure kWh used if I heat the office via GCH single room via evohome. Our gas unit price is under a third of electric (33.76p vs 10.28p).

Not entirely sure how I can work it out with any degree of accuracy to compare heating the one room for WFH with my 650w oil-filled versus GCH via evohome.

Smart meters, I guess.

No figures to back it up, but my thought was running the GCH just for one room is less efficient and costlier than what I’m doing. However, when other rooms/zones have their programmed heat on (kitchen and family area before school) I’ve got the office zone ‘on’ then to give the room a boost. Room I work from is far less than ideal being north-facing with 1.5 external walls, high-ceiling stone-built mid-late1800s, but it’s all I’ve got available to me.

If you listen to that BBC thing above though it states that all the portable solutions cost roughly the same to use in the end. ie an oil rad is just as expensive as a fan with heating element (which feel more expensive)

Isn't the problem for most WFH people, myself included, the fact that you're sat still on your arse and not moving around all day? Same as sitting on the sofa infront of the TV on an evening. I've found that if I get too cold then even just getting up to walk around and make a coffee or running up and downstairs a couple of times makes a big difference. Walking the dog on a lunchtime keeps me good for a couple of hours afterwards.
My home office is only an elaborate cupboard with a window at 1.2 x 2.1m, just big enough for a desk and chair pretty much. We had it built recently as part of an extension and I purposefully kept it small so it would be easy to heat. Just keeping the door shut means that it is about 2 degrees warmer than the rest of the house after a couple of hours just from my body heat and background computer heat (only a laptop and 2 monitors so not a huge amount).
I did have the fingerless tramp gloves on yesterday morning though on what felt like the first properly cold day.

As I'm the only one at home today I tried using the GCH instead of my oil-filled radiator. Not what I expected.

Last week: 650w electric oil-filled radiator under my desk to heat me for 8hrs like I've been doing the past couple of years (estimating 50% actually drawing power with the thermostat clicking on and off):33.76p/kWh = (0.65kW x 4hrs) x 33.76p = 87.78p/day*

Today: GCH** to heat only the room I'm working in, no other gas use in the 5hr period 8.30am-1.30pm, used 1.923m3 gas = 21.85kW of gas in 5hrs. 21.85 x 10.28p = £2.25 for 5hrs only, that's not my full working day! Outside conditions around 2degC colder than the day I compared with last week although it's pertfectly still compared to a tad blowy last week, that's surely not enough of a factor to account for that difference.

I think I'm back to using the electric heater now that I know.

* No smart meters or plugs here and too much other leccy use to be able to isolate my oil-filled radiator use, hence me estimating the power usage based on rated power.

** Glow Worm Betacom 4 30C boiler, 30kW, ErP 94% A rated, new in Nov 2018, with Honeywell evohome controller with all rooms zoned except bathroom and WC rads.

My home office is only an elaborate cupboard with a window at 1.2 x 2.1m, just big enough for a desk and chair pretty much.

That's what I'm heading towards. Current 'office' is 4x3m-ish, high ceiling, large DG windows and doubles as a gym/storage/dumping ground. Trying to convince Mrs a11y we empty the upstairs 'cupboard' so I can stick my desk and chair in there: 1.9 x 1.8m, partly under the eaves with a small, ancient single-glazed skylight. That's got to be a more sensible (efficient) approach.