When asked your question, liturgist Thomas Richstatter, O.F.M., replied, "I would refer you to The Postures of the Assembly During the Eucharistic Prayer, by John K. Leonard and Nathan D. Mitchell (Liturgy Training Publications), regarding the practice of kneeling at prayer.
"Regarding kneelers as furniture, I would presume they were relatively late. Originally there were no pieces of furniture for the 'circumstantes' (those standing about), simply a chair for the president. As a concession to the infirm, stone seats began to be attached to pillars, or to the walls. By the end of the 13th century many churches in England appear to have some wooden benches—often called pews.