This is a great question!
My answer... there is no one size, fits all furniture item because it all depends on what YOU are into.
If you enjoy a good spanking, I would recommend a spanking horse or, if you're looking for something a bit more inconspicuous try a Liberator Chaise Lounge or Tantra Chair. If you are partial to being bound try a bondage bed. If the space is minimal a St. Andrews Cross could be a better, space saving choice. If you like role playing you may want to invest in giving your room a boudoir look by including a 1940s style vanity with stool. These are just a few options.
The best part about this question is you're going to have so much fun tapping into becoming aware of what you enjoy when you're feeling intimate. That will be the key.
Remember, if you need additional help building your arsenal DM me here and let's design something intimate, fierce and WOW together!