Associate
In that sort of space, you're probably better off going for a direct blown hot air heater, and have it on a very low setting, but directed straight at you.
As the space isn't enclosed, and you've said a draft comes up the stairs, an oil radiator isn't going to help much, as it's trying to heat the whole space, whereas a hot air heater will be blowing warm air at you (so you'll feel warm), but will never actually heat the space.
As the space isn't enclosed, and you've said a draft comes up the stairs, an oil radiator isn't going to help much, as it's trying to heat the whole space, whereas a hot air heater will be blowing warm air at you (so you'll feel warm), but will never actually heat the space.