I would never do anything to discourage people from stopping smoking but I, like quite a few people, replaced smoking with food when I quit. My lung health improved dramatically (knocked eight years off my lung health according to my asthma nurse) but my waistline got chubby.
A few pounds went on and I decided that as I had successfully quit smoking using this fantastic forum I would use a forum to get fit. That led me to myfitnesspal.com
Whether you want to lose a few pounds or take up a new sport or exercise, there is something for everyone. You can track your calories (there is a database which you can even link to your phone) and exercise and there are private friend sections (a bit like Facebook) as well as public forums.
Since stopping smoking I've taken up running, climbed some of the biggest mountains in England and have increased my fitness tenfold. I'm in no way connected financially or formally to MyFitnessPal (MFP) but can wholeheartedly recommend it. There is often also talk about quitting smoking and lots of people to offer support.
I just wish I had known about it while quitting as I might have been able to keep my weight steady when I first stopped.
Wishing all the best in quitting - an amazing thing to do and you will be so proud of yourself!