Bed size

I read that someone used a queen size mattress in the king size space so that there would be space on each side to put "stuff" like clock, radio, and sundry other things one might like to have handy at night. Sounded like a good idea until.......I read in another thread that owners experienced cold coming up from the sides of their beds which they solved with towels, swimming pool tubes, etc.

If I order a queen size mattress for a 3124kb, will I be making a mistake because of cold? Or is the size of the mattress irrelevant to this problem since the cold comes through gaps rather than through the bed platform itself?

Thoughts about this?