I was told by my “Chosson rebbe” that having beds of different sizes is a lack of tznius, vehamayven yavin. My Rosh hayeshiva zt”l was against larger beds but i only found this out after I purchased mine. As always ask your LOR or halachic advisor.
It depends on the size of the room. Most young couples get at leas 48″ beds today if they can’t fit full size. I don’t know of any young couples who still purchase twin size beds.
