How I did it (also around your age, smoked since young, overweight) was changed only my eating habits first. NOT calorie counting, but swapping junk food for food with nutritional value. Did that for a few months to let my system adjust. Then (spring time by then) I went out for gentle walks EVERY day. 10 minutes at first. Then 15, 20 and so on. When I could walk at a gentle pace for 30 minutes, I started to up the pace. Just gradual increases, and slowed down when I felt short of breath or uncomfortable. So maybe a short 'burst' of speed for a minute then a minute at a gentle pace. I didn't time this, I listened to my body and adjusted accordingly. Over time, I found I could walk for 30 minutes at a brisk pace without any breathing issues. I can't stress enough how gradual this increase was.
I'd agree that yoga (a hatha yoga class, not a 'gym bunny' yoga class) helps with the breathing/lung capacity and heart/muscle function too.
In the meantime, I banned myself from smoking in the house or the car. Then I stopped taking my cigs out with me on short trips (under an hour) out of the house - I mean, if I was THAT desperate for a cig when I was out and it couldn't wait then I could just go to a shop and buy some. Then I delayed my first cig of the day by 10, 15, 20 (and so on) minutes. Did other stuff to distract myself from the craving and obsessing about it.
Then I got a horrendous chest infection literally out of nowhere (what I'm now convinced was covid as it was the Xmas before the first lockdown) - I couldn't breath yet I was still trying to light a cig up and I just had 'a moment' of What The Fuck Am I DOING? Why does this little stick of leaves have such a hold over me?
I won't lie, I had a few false starts (or stops) but each time I started smoking again, I felt disappointed in myself, at how far I'd come just to 'ruin all the hard work again'.
I lost 4 stone and now regularly walk 8-10 miles with my walking group. Something I'd never imagine being able to do, once upon a time.
TLDR; small changes, start slow, listen to your body, increase gradually, delay and distract.