Grieving the loss of my mom and finally hitting rock bottom

How do you eat an elephant? One bite at a time.

Don't try to blow up your whole routine and rebuild it all from scratch on day one. Focus on small, sustainable changes, one at a time until it's second nature, then make another change. I don't think the Slimfast is necessary but maybe it will work for you, that's very individual.

I would begin by just trying to log honestly, without worrying too much about staying under budget. That will be the goal eventually, yes, but for these first...let's say two weeks, your main focus should be on just building the habit of logging your food, period. You could even start by writing it down on paper rather than using the food diary in the app, if seeing the numbers will upset you; cultivating mindfulness is the name of the game right now.

If you're not currently measuring your servings, start doing that, too - get some measuring cups/spoons at least, and ideally a food scale (they're not expensive, you can pick one up for $10-15 at the grocery store, probably). The first main goal is to get an idea of how much and what you're actually eating, as well as gathering data to see what your next step should be. Pick one simple thing to focus on; do that for a week or two until it's ingrained; then pick another simple thing to focus on. Examples are things like swapping soda for water, using less creamer in your coffee, using chicken or turkey instead of beef or pork in a recipe, or trading a higher-calorie snack for a lower-calorie one.

Pay attention to what happens after you make your simple change to figure out what works and doesn't work for you in terms of satiety. Some people do best with plenty of protein or fat and are OK with a smaller volume of food; others need a larger volume of food to feel full, so they load up on fiber by way of vegetables. For weight loss the important thing is eating less than you burn (CI>CO), but satiety is what allows you to do that, and what you find satiating varies from person to person.