You'll need to explain what the concept of a king-sized bed actually means to you in The Sims 4 before anyone can answer that question.
The work a creator would need to do is very different if you just want it to look good in a build vs. if you want someone to try to make all the animations look decent when Sims use it vs. if you want a third Sim to be able to lie down on it. There's also the question of whether everything you want is even plausible based on currently known capabilities at all (e.g. since we can't get two Sims to cuddle in their sleep in an existing EA bed, getting a triad to do it, or parents to cuddle a child in between them, isn't going to work with real interactions either, only static posepacks).
(ETA: The note about the bed in the second set linked above touches on some of those points, in fact.)
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