Alexandra,
With very low temperatures you would risk freeze damage to the bulb, which would either kill the bulb or destroy tissue and leave it open to disease. I would think that the hot water treatment would be safer for your bulb at the temperatures previously specified in a prior reply from another lister.

Since you only have the one precious bulb, I'd steer clear of potential freezing.

Have you experimented with trying to maintain any hot temperatures with the various methods discussed?
K

I considered trying the hot air method with the oven (I got an oven thermometer) but was scared...

Then I realized I could leave the bulbs on a heater which goes up to 50C on the surface and I did leave them there turning every few hours. The bulbs got a little scar on one side but this is all. (I visited an organic gardenshop and "rescued" 3 rotten bulbs which were being sold at 0,5 euro each; now I have 4 bulbs and I wonder wether it was the right thing to do since I have no experience at saving a bulb from rot) Poor them have flower scapes. They are all hard but rather small (1-1,5 inch diameters) The heat treatment didn't seem to bother them much at all.

Should I cut the flower scapes or should I let them bloom and go to seed to save them through seed...?

Foliar feeding would be allright (kelp based feed)? Or should I refrain from any feeding? I dusted them with rooting hormone and put each on top of hydroton balls with 0,5 inch between the base of the bulb and the water which is 2 inches deep. Pots - transparent water bottles. I made the mistake of covering the hydroton and the top of the bulbs with clear plastic film because the top hydroton layer was dry.