CoachL pointed me to something new. TumblTrak sells an innovative product I have not yet tried:
ULTIMATE STRAPS
The Ultimate Straps securely attach a gymnast to a strap bar, without the need for several different sizes of straps. Includes two PVC tubes.
Ultimate Straps are fully adjustable for all sizes and the double buckles with the velcro system are very secure.
I cannot coach without safety straps. The biggest headache with using them, however, is getting a good fit on different gymnasts.
This would solve my last problem.
More information on training with strap bars.
Gymnastics Coaching.com 