If you really want the "whole experience," just buy a used copy of the oldest edition. Maybe you'll get lucky and some maniac back in the 1960s scribbled cryptic notes on the margins.

I'm a big Chambers fan, so I went and looked at Amazon, and they all look the same to me. There are no problems of translation, so I'd say the one with the coolest cover art is the one you want.

This one is pretty good:

http://www.amazon.com/The-King-Yellow-Robert-Chambers/dp/1497442966/ref=sr_1_2?ie=UTF8&qid=1400258417&sr=8-2&keywords=%22the+king+in+yellow%22+chambers

This looks dreadful:

http://www.amazon.com/The-King-Yellow-Robert-Chambers-ebook/dp/B00IK08LVC/ref=sr_1_6?ie=UTF8&qid=1400258417&sr=8-6&keywords=%22the+king+in+yellow%22+chambers

and this is just cheesy:

http://www.amazon.com/King-Yellow-Other-Tales-Terror/dp/1496096320/ref=sr_1_4?ie=UTF8&qid=1400258417&sr=8-4&keywords=%22the+king+in+yellow%22+chambers