Question:
If a husband and wife are not in a state of Niddah, must they nevertheless separate their beds before Yom Kippur?
Answer:
Yes.
On Yom Kippur, Chazal required a husband and wife to observe the laws of Harchakos as a safeguard against marital relations, which are forbidden on Yom Kippur. Accordingly, they may not sleep in the same bed, even if both remain fully clothed. Furthermore, separate beds may not touch each other, just as by the laws of Niddah. Therefore, a couple should remember before Yom Kippur to separate their beds so that they are not touching. The same restriction applies both by night and by day throughout Yom Kippur.
Conclusion:
A husband and wife should prepare before Yom Kippur by ensuring that their beds are separated and do not touch each other. This is part of the Harchakos observed on Yom Kippur to distance oneself from marital relations.
Sources:
Admur 615:1; Michaber O.C. 615:1; Mordechi Moed Katan 934; Taz 615:1; Mateh Ephraim 615:1; Mishnah Berurah 615:2; Kaf Hachaim 615:5. The requirement to observe Harchakos on Yom Kippur and not sleep on touching beds is explicitly brought in these sources.