The status of niddah has two separate aspects:

First, a woman during niddah is t’meiah – ritually impure. This has no practical implications nowadays. Therefore, your friend’s statements about sitting on surfaces are not at all applicable today. It will not be possible to practice the laws of tumah and taharah (ritual purity) until the beit hamikdash (Temple) in Jerusalem is rebuilt.

The second aspect concerns the permissibility of physical relations. This does apply today – no physical contact is permitted between a man and a woman while she is niddah. There are some practices, known as harchakot, that are designed to prevent inadvertent touching and apply specifically between a wife and her husband (as opposed to other men). These include sitting on the same soft surface (such as a couch) or the same moving seat (such as a swing). See the articles in Conduct while Niddah for further information.