I've been struggling to do this for years. Previously, the longest I ever made it was 15 days with the Insight Timer app. Its shows you how many days in a row you did and it's very encouraging.

What actually got me to do it for longer, and without any willpower, was pirating Sam Harris' Waking Up course.

This is because I already had the muscle memory for going through audiobooks and podcasts on my phone, so I'd just open up VLC every night and instead of a book I'd listen to a guided mindfulness meditation. I did 150 days in a row.

The course is 50 days and I just started over when I was done because I liked it so much.

If I actually got his app, I don't think I would have been as successful, I think it was really the muscle memory in my thumb that opens VLC every evening to listen to some relaxing audio that got me through it.

The course itself is highly recommended: I've been meditating for years but with different methods. With Sam's guidance I made more progress in a few weeks than I've made in years.

Also worth mentioning, if you can't afford it, you can email him and he'll let you have it for free.