I think most or all of the manufacturers make a belt that is designed to work well with their bags/appliances. So for example I always wore Hollister and I wore a Hollister ostomy belt that was compatible with Hollister pouches.
I don't think the ostomy belt needs to have any bells and whistles, as long as the material is comfortable, it fits securely onto your pouch, and doesn't irritate your skin.
Your insurance may cover a one time purchase of an ostomy belt -- mine paid for one for me (I ordered it through the mail order pharmacy that provided the rest of my supplies).