was wondering the best beans to use in therapeutic bags that you can heat &/or freeze that don't burn & smell
Even the synthetic store bought ones can burn and get smelly... I'm going to make some with lentils this year (to replace our burnt, smelly store bought one). Someone claimed that they retain the heat longer than rice and they are a nice small size so won't be too bumpy.
Any of them can burn. But I wouldn't use beans if you're planning to freeze.
You could always try buckwheat hulls (I can get them at the local HFS). But typically I just use rice. And expect the first half dozen times you use it it's going to be damp (you can minimize this by baking the rice on a sheet pan for a little while on a low heat).
Field corn is another one that I've seen used - not popcorn, but the type of corn that is ground up and fed to cattle (find it at a feed store).
But any of them will burn if you overheat them.