IWTL how to stop oversharing and limit some information

I am 30 years old female. Ive never had a true friendship. All of the previous ones were really toxic and left me traumatized for years on end. I have a mental illness and I still hear the voices of people from the past.

The problem is that I dont have proper boundaries and I tend to overshare a lot even without sensing it. Once I start talking to someone I am like an open book. That person, if they are friendly, can receive any type of info - whats my job, how much i weigh, what i did to lose weight etc. It pisses me off because people are so mean nowadays they lie and hide stuff out of hate, but I am like a total fool who doesnt know what to say and what not to say. I know women can get so jealous not to mention they like to copy everything i do.

I read a book or 2 about boundaries but I feel I will need to start taking notes and I have no clue how to set them yet. I panic and get scared as if reading a self help book is a case of life or dead and my life depends on it.

How do I learn whether I should share something or not? How do I know what to say if the other person asks me something?

My whole life I have only used my gut feeling without much thinking.