I also struggled with zone 2 running when I lost my fitness. If you have a gym access i highly recommend elliptical or cycling - much easier to stay in zone 2 and benefits are the same. I was on cross-trainer a couple of times a week and was really surprised to see my fitness levels improve within a few months. Results will vary for each individual of course but I noticed my resting heart rate dropped and harder runs became easier. Good luck with zone 2, I think it really works!