Waist trainer help

For the moms who already had their babies and use waist trainers/cinchers I need advice , I bought the kind that hooks, like bra hooks, and when I put it on its fitted/tight on the bottom but really loose at the top , like i can put my whole hand in it. Does that mean i need to go down in size?? But then it'll be so tight on my stomach i probably wouldnt be able to close it. Any advice is helpful