I agree. leave them where they are now until spring proper. If you think they need a bit more shelter then you can wrap them in old net curtains or buy a roll of frost fleece. What you put in the hole when you plant out depends on the quality and type of your soil. In good deep well cultivated soil, then nothing needed except maybe some slow release fertiliser. If your drainage is poor, add gravel. if you soil is sandy then plenty of compost, either home made or tree and shrub compost bought by the sack.
I give mine the rolls royce treatment and, as well as compost, put a mycorrhyzal fungus preparation and water retention gel crystals in the hole as well to give the plant the best chance to get away and also a water reservoir at the roots because my clay soil dries out rock hard in summer and I am on a meter and can't go around watering like a mad thing.