If you're going to spend money on it, in a bathroom going with under-floor low voltage radiant under the tile has the best overall comfort factor, and beating any baseboard convector or wall radiator considerably. Next would be radiant ceiling (which doesn't have the floor leveling issues), followed by cove-radiant heating.
Without a heat load calculation it's hard to say how much of ANY type of heater it really takes. Got some U-factors and square footage for the window & skylight? How about the R-value of the SIP & attic insulation,
Cove heaters look like this:
They work like this:
Basically, a radiant cove brings every surface in the room up to about the same even temp. A cove heater that fits over the window would balance out the low radiant-temp of the window would be ideal, since the window is typically the lossiest & coldest surface in the room, and putting the cove heater on that wall directed toward room, it makes the average radiant temp of the exterior wall "feel" like the warmest part of the room rather than the coldest. And it makes the room also feel warmer than the air temp would indicate. Some people even control them with occupancy sensors, using the thermostat only to inhibit the heater from turning on when the room is already warm, rather than maintaining the room at a setpoint. They come on fast, and even a 60F room can feel pretty comfortable in under a minute, long before it's actually reached the thermostat's setpoint.
They're pretty simple & cheap too- comparable to finned electric baseboard pricing- I can't imagine anybody opting for electric baseboards after experiencing cove heating. Same money, but world of difference on comfort, and cheap to operate too, if you take an occupancy sensor approach, with a line-voltage thermostat in series with the feed to the cove heater to keep it from overheating the room.
In some ways it's better to oversize a cove-heater for the peak load if you run it in occupancy sensor mode, but with very low heat loads almost any cove heater would meet that description. A typical three-footer puts out about 1500 BTU/hr for about $75 USD. A four footer is good for about 2000BTU/hr at about $100. With 8' of exterior wall a 7-footer might be appropriate, which would be good for about 3500 BTU/hr, but is still in the $150 range. Estimates are from this vendor, but there are others. Odds are you'll get out for under $200 no matter what wattage or length.
You have to pay attention to the wattage, and select an occupancy sensor that has some margin over the power draw of the heater. Most cheap box-store occupancy sensor wall switches are rated at 500 watts or less, and not appropriate for this application. Similarly the line voltage thermostat needs to be up to snuff, but even bottom of the line $15 versions usually have more than enough for what I'd anticipate here.