Here is the main reference to the issur psakim against smoking. The sefer is called “Chaim Lelo Ishun” written by Rav Yechezkel Aschayk, published in Eretz Yisroel several years ago (publication date is missing). The letters of haskamah are open and specific. The haskamos are from: Rav Shteinman, Rav Moshe Shmuel Shapiro, Rav Michel Yehuda Lefkowitz, Rav Shmuel Halevi Wosner, Rav Nissin Karelitz, Rav Yerachmiel Gershon Edelstein, Rav Boruch Dov Povarsky, Rav Matisyahu Salomon, Rav Shimon Bedny, and Rav Yitzchok Zilbershtein. The other names listed in my previous are quoted in the text of the sefer. Most include the exact language. There is also a letter (dated Menachem Av 5764) that concerns the issur to begin the smoking addiction signed by Rav Moshe Shmuel Shapiro, Rav Michel Yehuda Lefkowitz, Rav Aharon Lein Shteinman, Rav Shmuel Auerbach, and Rav Nissim Karelitz. Rav Elyashiv added his signature to that letter. It is true that this letter addresses the issur to begin smoking, but it also states clearly that smokers must wean themselves off of it, and should never smoke in public places where it can bother others. However, in contrast to an earlier comment, this letter does NOT state that it is muttar to continue smoking because it is a tzorech. I request a reference to such a statement from Rav Elyashiv.
I also call attention to an earlier sefer “Pe’er tachas Efer” that addressed the issur against smoking.
There is also a lengthy psak about the issur against smoking issued by the RCA. This psak discusses all earlier teshuvos from poskim on the subject, including the parameters of “Shomer psoyim Hashem” which was mentioned in one psak from Rav Moshe Feinstein. This RCA psak is available online.