I sell tshirts, and it took me the longest time to figure out how to wrap them nicely. I think I have finally figured it out.
I roll them tightly so they aren't all loose, and they fit better in the mailer. This shows off my applique work, too. After rolling, I tie them with a pretty ribbon, and add a card with just my shop name. I then wrap in tissue paper, tie with twine and add a shop sticker with my logo. In the mailer, I include a small glassine bag filled with a thank you card and my business card.
Since you also sell loose, bulky things, folding and rolling might work for you.