Under what circumstances may a husband or wife sit or lie on the other's bed or couch when the wife is a Nidah?
Halacha forbids a husband from sitting or lying on his wife's bed during the period of Nidah, even if she is not present. The only exception to this rule is that a husband may sit or lie on his wife's bed once she has left the house to go to immerse in a Mikveh. Since she has already gone to divest herself of her Nidah status, and will soon return home, it is permitted for the husband to sit or lie in her bed.
A wife, by contrast, may sit or lie in her husband's bed during the period of Nidah, but only in his absence. If he is present in the room, she may not sit or lie in his bed. Under circumstances where a wife has a particular need to sit or lie in her husband's bed, then, according to Chacham Ovadia Yosef, there is room to permit her to do so even in his presence.
These Halachot apply only to beds. Couches, which are used for sitting, rather than sleeping, are not included in this prohibition. Therefore, a husband or wife may sit or lie in any couch in the home during the period of Nidah.
What is the status of a couch that one opens at night to convert into a bed? May a husband sit on a couch that his wife uses as a bed at night?
Chacham Ovadia Yosef ruled that since the couch must be opened to become a bed, we may consider the couch during the day as a separate entity from the bed, and thus a husband may sit or sleep on the couch. Preferably, however, the husband should use the top mattress of the couch for sleeping at night, so that the couch could certainly be considered his bed, rather than his wife's.
It must be emphasized that in situations where it is permissible for a husband and wife to sit on the same couch during the period of Nidah, no physical contact between them is allowed whatsoever.
Summary: A husband may not sit or lie on his wife's bed when she is a Nidah, except after she has left for the Mikveh. The wife may lie or sit on the husband's bed when he is not present. If a couch opens into a bed and the wife sleeps in it during the night, the husband may sit or lie on the couch during the day.
(Based on Halichot Olam, vol. 5, p. 110)
