Daughter getting into diaper

Hey so recently my 20 month old has been getting into her diapers. We have tried putting her in footy pjs and onesies and everything but she is still finding a way to get into her diapers. We want to start trying to potty train but I have no idea how to start. I feel like putting her in underwear might only make it easier access for her. Did anyone else go through this? How did you get through it? She keeps getting into her poopy diapers and my husband and I are just done with it.