I think most humans who are wishing to change something significant in their lives probably suffer attacks of self-sabotage. I sure have, many times.
I have realized it doesn't help to start labeling it as laziness, complacency, or other negative characterizations. Those just depress me and eat away at whatever determination I have to be kinder to myself. For me, it's far more effective to think of the old and the new as each having its own hierarchy of needs. Needs are all valid, but they don't all carry the same weight (no pun intended).
So I will list the needs (at least mentally) being expressed through an old habit that is trying to reassert itself. I give it some time, let my mind run over, under, around and through to make sure I have as many needs listed as possible. Then I do the same thing for the new.
Some items on each list are pretty evenly matched in importance, which can create quite a bit of tension. When this pull is unrecognized, one particular need of the moment has a chance to stage a coup. For example, "comfort," right now while I'm feeling tired, discouraged, lonely, whatever, might trump better health, more energy, a happier me, when I look in the mirror next week. There's a lot of power in "now."
But if you have the lists of needs firmly in mind, you can often shift your attention back to the needs you have projected into your precious future, and pull them into "now." And at the same time, you might realize that a cup of hot tea with a spoonful of honey, or calling a friend, or some other back-up plan, may work nearly as well for your immediate need for comfort as a pint of Ben and Jerry's (or your temptation of choice) consumed in front of the TV.
Does this always work for me? Nope. I'm human, and sometimes I'm tired and unmotivated. But one day's failure does not have to undo a week or three of effort. I forgive myself, decide whether I will carry my new list forward tomorrow, and then do it. (And by the way, for me it's not a decision to "try" to do better. It's a decision that I "will" move forward assertively. "Trying" accomplishes very little, because there's a built in failure button just begging to be pushed one more time.)
Wishing you success, one moment at a time!