Perhaps the only discipline you need, is that required to form a single habit.
While there has been a long standing rumour it takes 21 days to create a habit, this is a rumour based on Dr. Maltz's suggestion in his 1960 book Psycho-Cybernetics that it takes 21 days to get used to your new self after an operation or medical issue, such as a nose job, or having lost a limb, not about habit forming directly. "These, and many other commonly observed phenomena tend to show that it requires a minimum of about 21 days for an old mental image to dissolve and a new one to jell." This quote has been spreading throughout the self-help community like a viral version of the telephone game for decades.
The one scientific paper I can find suggests, with prediction modelling, it takes anywhere from 18-254 days to form a habit. On average, it takes 66 days. Based on this, you should be able to form between 1 and 6 habits year. I would suggest you start with one small habit as a goal small, and not punish yourself while developing your habit. Making an error or two will not have a long-term impact. That being said, the reward for discipline on this one small thing, for this short term of building the habit, will be extremely rewarding.
Trying to do to many things, or even too many steps in your habit, is designing for failure. Pick one thing you know is achievable for you if you put your mind to it. Do that thing regularly, for the next 66 days. At 66 days, evaluate. By the end of the year, you'll see yourself a whole new person, even if you've only developed one simple new habit. You'll have improved your previous self, which is the ultimate measure of success, to me.
In the book The One Thing, Gary Keller writes, "Australian researchers Megan Oaten and Ken Cheng have even found some evidence of a halo effect around habit creation. In their studies, students who successfully acquired one positive habit reported less stress; less impulsive spending; better dietary habits; decreased alcohol, tobacco, and caffeine consumption; fewer hours watching TV; and even fewer dirty dishes."
So even by working on creating one small habit, it will have a ripple effect in regards to improving your life.