It has been said that declaring an intention of trying to give up smoking is the same as saying you will fail - it is as much as a foregone conclusion. But those who say little or nothing, just stop abruptly as a result of a firm decision, are the most likely to succeed. I know a number of the former, almost all of whom restarted (sometimes months or even years later) or never really stopped. I also know several of the latter and (to my knowledge) they never re-started, including those whom I did not get to know until sometime after they had stopped.
The ill effects on health from smoking, even if it does not kill you outright, are so well known that it is astonishing that anyone should take up the habit - as you have said, the stink alone should be enough to put you off. I know that for me "Eau de Fag" is the one scent that completely spoils the allure of an otherwise attractive woman, it is utterly revolting and a whiff of dung would be better. My father smoked, died of smoking related illness, and I still miss him. I was never remotely tempted to take up smoking although at the urging of a friend I stole some from him and tried one out when I was perhaps around 10 years old. It was such a disgusting experience (one or two puffs) that I never tried again. Years later, when I met my wife to be, I told her bluntly that unless she stopped smoking I would not come near her - I said the thought of licking the inside of an ashtray was repugnant. We will have been married 41 years next week - more than 42 years ago she made a choice and stopped, permanently. Everybody is capable of making a decision and sticking to it, rather than diving into self-indulgence (self-pity ?), and so can you. This should be one of the easiest choices to make. Stop now and never look back except decades from now - then actively seek out those who are dying from smoking and think how you are your own living saviour from that.
As for gaining weight, that is tackled the same way, by determination. Once a year every year we meet the same woman because we pick blueberries at her farm - in fact we were there on Sunday past. What we noticed was something that astonished us - she had lost an awful lot of weight because last year we noticed how she had put even more on than before, she was undeniably fat. Now we were greeted by an attractive woman, one we recognised from ten years or more back. She explained that 18 months ago she and her sister joined a class headed by someone who organises these things in the wider area around here. Since her maximum weight she has lost 23kg and that is an awful lot. What is most amazing is that it has not been done with some crash diet and certainly not with surgery. It has apparently all been done by managing her food intake, the quantities and the mix of the various components. She looked not only good but very healthy too - utterly admirable, and we told her so.