Thanks all for your suggestions! So here the results of the items we tried! Smart Bones, edible Nylabone, and NBone Natural Teething Ring all proved to be WAY too soft for Leo's Chew-abilities! He won't touch the non-edible Nylabone. The three items he LOVES are
1) Organic Hemp rope toy - this was recommended as opposed to cotton because he hemp is digestable if he happens to rip off a small string
2) Earth Animal No Hide - made from all natural ingredients and they take a WHILE for him to chew.
https://www.earthanimal.com/p/no-hid...-7-inch-chews/
3) Bully braids (essentially a bully stick but small) - they're small enough for his mouth, and I watched him closely, they do soften as he chews. This may not be an "all the time" chew for him, but they seem to stand up to his chewing but not be too terribly hard for his teeth.
https://www.chewy.com/bully-sticks-b...E&gclsrc=aw.ds