Maternity sizes

Morgan • I`m Morgan Cheyenne and have PCOS and am pregnant with my first child. I am due May 4th. I am extremely nervous and petrified but at the same time am very blessed I have even gotten to enjoy this.
I know everyone's bump is different but I was looking at some maternity clothes on eBay and I have no clue how to estimate what size I'll need. I'm already big so I just don't know. I just wanted to know about yalls experiences. Thanks