Hello and welcome! Here are a few things that have helped me:
My biggest weakness my entire life has been sweets, especially late at night! There were more nights than not that my husband and I would make cookies, go get ice cream, etc. I stopped buying those sorts of things and ate some of my favorite fruit if I wanted something sweet. It usually was enough to satisfy me, and now, I very rarely have those cravings.
To help counter the smaller portions adjustment, I've tried to incorporate healthy snacks between meals into my day. It helps to keep me from ever getting to the "Oh my gosh, I'm STARVING!" point.
If you fall down, whether it's one cookie too much, or one bad day, week, or even month, try your best to put your energy into taking a step forward with the next, tiniest choice. The next bite, the next meal, etc. There are always going to be bad days - it's a part of life! - but know that you CAN do this! Yes, it is discouraging when you take a few steps back, but you are still miles ahead from where you were. You've got so many people here to support and motivate you!