I need to get serious about losing this weight

I'm 20 years old, and I currently weigh 350lbs (158kg) at 5'9ft (175cm). I've ALWAYS been heavy, literally since I was a toddler, and back in my senior year of high school, I went from 300lbs to 250 within a couple months due to a bad eating disorder that almost sent me to the hospital.

I got into a relationship, gained some weight to where I was about 287lbs and then I got pregnant, and rocketed to 330lbs. My postpartum cravings were the worst for me, as all I could think about were specific junk foods to the point I'd practically obsess over them.

I'm now 6 months postpartum, and EVERYTHING hurts to do for obvious reasons. I'm embarrassed with how long/hard it is to get up off the floor after playing with my son, how I look when I'm about to go swimming, everything. I need to get healthier for myself, and most importantly my son.

I'm about to move upstate to an apartment on the 5th floor. I intend to go up and down the stairs every day, or at least every other day and go on a diet of no more than 1,500 calories a day (for sure going to have slip ups).

I need advice for meals, and exercises I can do without being so sore it discourages me from being consistent. Whenever I workout, I end up going to the extreme and doing as many as I physically can, to the point of 80 squats (at 350lbs it's a lot), just to name one of the examples. Going to the gym isn't an option, but I intend on swimming a lot.

I don't want to end up like my father and dying at 48, and by the way I'm going, it'll be sooner than that. My goal is 190lbs-230lbs, hell, even 240lbs. Any advice is appreciated..