i had a similar problem with my nyckelharpa which had a strap which went across my neck and over both shoulders. I got a slider strap is a figure 8 instshaped strap which distributes the weight. often used by conga or djimbe players as well as wind instruments an others...see this:
www.slider-straps.com/

i also came across this when searching for that link http://www.darestrap.com

i am glad you found something that worked for you.
quick! patent it!