You know what they say: Big screen, big inspiration from your favorite adult-audiences entertainment. Cushy couches, deep-pile carpet, abundant pillows and throws, wood-burning hearth—sure, they're cliches. That's because they reliably seal the deal. Don't forget a wet bar to help loosen inhibitions. And soundproofing your pleasure pit may be smart so neighbors won't get a thrill. Bonus tip: Consider adding a motion-sensor alarm on the stairs in case the kids sleepwalk.