RE: Thumb release suggestions
Carter's Chocolate Addiction works for me. Some say that you need larger hands for it, but I've not found that to be the case. My hands are not large and for me, it's quite comfortable.
It has adjustment for both travel and tension. Also, some of the later models have easy access to springs so that you can change the tension by changing the springs.
I shot some of my best scores in league this winter with mine.
This is only a suggestion. A release is one of those things that's very personal. You need one that fits you and your shooting style.
The biggest negative is the cost.
Another possible negative is the lack of a safety. A lot of people want that, but for me, a safety is an added complication. I just draw with my thumb behind the trigger.
Hope this helps,
Allen