One possibility might be to start with books written for young children ("early readers"), which also assume a more limited vocabulary. Then gradually ramp up to books written for somewhat older children ("middle grade") before returning to books written for adults ("young adult" fiction typically isn't written much more simply than fiction for adults; it's just that the themes and characters are aimed at a 12-17 year old audience). That's how most native speakers learned to read.
There's plenty of fiction written for these demographics. Unfortunately, nonfiction is mostly limited to biographies and very basic textbooks. You won't get business books in these categories.
I also recommend reading newspapers, which tend to use fairly limited vocabulary and simple sentence structures, aiming for an "eighth grade" reading level.
Are you reading fiction or non-fiction?
One possibility might be to start with books written for young children ("early readers"), which also assume a more limited vocabulary. Then gradually ramp up to books written for somewhat older children ("middle grade") before returning to books written for adults ("young adult" fiction typically isn't written much more simply than fiction for adults; it's just that the themes and characters are aimed at a 12-17 year old audience). That's how most native speakers learned to read.
There's plenty of fiction written for these demographics. Unfortunately, nonfiction is mostly limited to biographies and very basic textbooks. You won't get business books in these categories.
I also recommend reading newspapers, which tend to use fairly limited vocabulary and simple sentence structures, aiming for an "eighth grade" reading level.