I agree with a vet visit and fecal to make sure there's no worms or anything to upset his tummy. Pumpkin can be handy to firm up stools on occassion but I think using it every day is just a crutch and it's important to solve the root problem.
One of our dogs had anywhere from runny to "pudding" poop since we got him, despite a few food changes. We did eventually switch to raw and it has been fabulous for him. His stools are firm and regular now, which makes for easier pickups, helps avoid anal gland issues, etc.
There isn't anything breed-specific in a raw diet, rather it's individual-specific. Your dog may need a bit more bone at first to firm his stools or you may be able to go back to a "regular" amount after the initial adjustment. Generally it's recommended to feed 5-10% organs, 10-15% bone, and 70-80% meat. You would want to give your dog about 2-3% of his ideal weight per day (so for a 50 lb dog that would be 1-1.5 lbs per day). I always recommend to start on the lower end of this range since feeding too much can also cause loose stools.
I would suggest to start raw with a single protein, many people choose chicken just cause it's easy, and feed that for a week or so (chicken quarters are handy). Then slowly add a second protein and feed the two for another week. Then add a third, eventually tiny bits of organ (they're very rich so you don't want to introduce them at the start). Between each step you want to have firm stools before you add something new - I think this will also help you identify quickly if there's a protein that doesn't agree with him. Don't give anything else at first, no supplements or anything.
I would say that most dogs have firm stools right from their first raw meal. But not all, so there may be some loose stools at first while he adjusts. I usually suggest to start raw when you'll be hanging around the house for the next couple of days, just in case he needs to go out more often. Introducing it this way also lets you get comfortable with it and do some research in the meantime.