Maggie 1K = about two thirds of a mile. It's 40 lengths in the 25M pool I swim in. A mile would be 64 lengths, which I am not aiming for.
I have never been to a gym in my life (well, since school days) but I love swimming, really love it so it is no hardship to me. And I do have a back that plays up from time to time & if I swim regularly it stays so much better, that it is worth it. And I am old & retired so can go at a time to please & don't have to rush to fit it in, which probably makes the biggest difference of all.
When you go back to the gym I think you will be amazed at how much more you can do as a non smoker.