Recommend a Good Textile Medium?

Hi. I print on shirts with acrylic paint and somebody said to use textile medium to protect it. I'm going to keep using acrylic just because I have a huge collection of paint and buying a bunch of fabric paint in the same colors is pretty expensive. So I was wondering what types to use. I use Palmer, Americana, Apple, Folk and Basics by Liquitex acrylic paints on cotton t-shirts with freezer paper or vellum stencils, so I'm not into screen printing or anything. What is a good brand and kind of textile medium? Also what does it actually do? Is it like a protective coating? I've never used it before so I'm curious. Thanks!