The idea of in-house separation (as it pertains to what I stated) actually came from a call that I had with a DBC. It made sense to me. Reading your post - also makes sense to me... and I would do it in two shakes of a lambs tail.
However, the actual bed in MBR is hers!
She bought it before we were married and before we knew each other (Yeah I know, it's old and needs to be replaced- eeeesh)
I could still do what you suggested and buy a new King bed for the MBR.
This would definitely upset her - but I see what kind of "upset" that it would bring on - truth - fact and righteous so she would see the reason without it going down as another mean thing I must have done.