To make as little impact as possible you should use as little resources as possible, so you should always choose cheapest, most artificial, mass produced versions of everything, including food, never travel, work as little as possible and only remotely. Basically be poor or at least act poor in every aspect of your life. Wear cheapest clothes and don't buy a new pair until they literally fall apart to the point that parts of you are sticking out that are illegal to stick out.
You might say that it's not a healthy way to live. That's even better, the sooner you die, the less resources you'll use. Don't breed of course.
If you are afraid you might have trouble sticking to your resolutions, then donate all of your wealth to something environmental and just move out of US into some poor country. It will do the bulk of your impact saving for you.