I'm inclined to agree with Joseph.
I have a lifetime in conventional building, and my rule of thumb is to make it stronger than you think it needs to be. "It might work" is a tad cavalier when considering potential catastrophic failure. A bed in the basement? I wouldn't sleep too soundly, myself. The worst case scenario makes it a foolish gamble. Actually, the other way round is ideal; rock basement, EB domicile atop, but you seem set.