John Gill Commentary Leviticus 15:20

"And everything that she lieth upon in her impurity shall be unclean: everything also that she sitteth upon shall be unclean." — Leviticus 15:20 (ASV)

And everything that she lies upon in her separation shall be
unclean
During her being apart from her husband, with whom she might be, and do all offices for him, but not lie with him; and whatever she lay upon during this time, bed or couch, and the clothes upon them, were unclean: everything also that she sits upon shall be unclean ;
chair, stool, etc. as is the case of a man, (Leviticus 15:4) .