I wouldn't feed yoghurt or any dairy product too often(plain all natural goat's milk can be a good idea though as well!)as dogs don't usually digest dairy well,as with most animals.A high quality probiotic would be just as good if not even better,depending on how many different probiotic strains there are in whichever you choose
The Jumbone due to poor ingredients could definitely be the problem,as treats are just as important as food to be careful with.I wouldn't feed them at all,regardless of age,but you could look towards bully sticks(sounds gross at first,but as long as they're just bully sticks with no additives and sourced from safe countries and not irradiated they're completely fine),high quality antlers,raw bones(never cooked as cooked bones cannot be digested properly),and Whimzees(not Antos which seem to contain wheat,again just be really careful with any product's ingredients)which aren't too long lasting for dogs but are still fun.
Slippery elm is an example of various natural remedies,one I unfortunately don't have too much experience with myself.You do have to be very cautious with some natural remedies though and make sure nothing is potentially harmful,as a lot of things commonly suggested can be unsafe when it comes to natural and homeopathic remedies(including pennyroyal often suggested for flea issues,which is not okay because it's quite toxic to dogs).Slippery elm is one of the safe ones though,definitely worth looking into
Also as a mini tip be sure no products you buy have alcohol(including denatured,ethanol,isopropyl substances,etc)as this is quite irritating and best avoided altogether.It goes as a tip for grooming products and supplements though,and potentially other things.