Breaststroke vs Freestyle

So, ever since I was a little kid, I've always been a breaststroke swimmer. I'm 57, recently cut back smoking cigarettes from a pack a day to about 4-5 butts a day, and can easily swim 1000-2000 yds a day without taking a break swimming breast, but can't even do a full length of freestyle without getting winded. I don't doubt the smokes play a role in this, but even as a kid this was an issue. Any advice as to how I might get better at freestyle?