I use a thumb draw but not a thumb ring. I started shooting several again years ago and couldn't do anything right. I was proficient as a kid but now couldn't hit the barn. Plus, the string was ripping my arm to shreds. I knew a little about Kyudo and knew they shot with a thumb glove and off of the hand on the opposite side of the bow from the English style. Well, I tried that and it worked and also eliminated any wrist slap. Because I'm cheap, I just used the cut off thumb of an old leather glove to protect my thumb. Just put a leather lace on it to wrap around your wrist to keep the thumb on your thumb. It works like a charm. You can also cut out a leather thumb ring and sew the ends together. Sort of like a 'finger tab' for your thumb. I've made several of these and they work just fine but I prefer the glove thumb. That's the only way I can shoot a bow now. (note: It the string is giving you problems even with leather protection, you can put a cloth insert inside the leather thumb for further protection - the thumb of a cloth glove). If you google 'leather thumb ring' you'll get great pics on some leather rings.
I bought a couple of plastic thumb rings from a guy from Europe on ebay and have tried using them. I need a LOT more practice with them. Shooting with a ring introduces a lot of quantum effects in my shooting.... arrows sometimes materialize to hit the target and sometimes materialize in the neighbors back yard.
You can also make thumb rings from 3/4 inch pvc pipe. Do a google search and you'll find a vid by a guy from Hawaii on how to make one.
From your description it sounds like you are using a thumb ring and shooting off of the same side of the bow as an English draw (the inside). Thumb ring shooters usually shoot off of the 'outside' of the bow so that the arrow goes across their thumb on their bow hand. That way, when your hand rotates into the arrow, the arrow is forced against the bow (not away from it). Rotating into the arrow is actually a part of the thumb draw and allowed horse archers to shoot from any position because their arrows always stayed on their bows. Hope some of this helps...
edit: Most of the planet used thumb rings and most of them were probably made of leather. I think the "English" draw may have developed because of the high draw weights of English bows.
The Chinese, Japanese, Mongol, Sassaniads, Romans, Greeks, Persians... all used thumb rings.
