Being on a budget, I haven't bought any "sex furniture" yet, but recently I got an ottoman (after measuring the distance from the floor to my belly when I'm on all fours - got to get the right height!) and a beanbag chair specifically for being bent over for various things. The beanbag chair is really handy, since it can be squished into different shapes, sort of. Neither one looks like sex furniture so I can leave them out in the living room . . . .
Also, when I picked out my bedframe I specifically got one that had plenty of spots that tethers could be attached.
And I second the "kitchen table" suggestion.