The halacha states that while the wife is niddah the couple should sleep in separate beds. While some poskim require a greater separation, the minimum distance between beds is enough that the beds and bedding do not touch. The separation should be sufficient to prevent inadvertent rolling over into the other bed. The beds do have to come apart; however, it is acceptable if they are attached to one headboard or footboard. Some couples prefer to have a large double bed and for one spouse (usually the husband) to sleep on a cot or twin bed during the period of separation. If you have some different arrangement in mind, let us know and we can tell you if this is also permissible.