Have a look on the Canine Arthritis Management website. Lots of advice and info on there and you can also join their FB page and support group. They have a whole section on supplements, where they discuss the evidence for each one. There are lots of videos with leading vets on there as well.
I did a lot of research, including on the CAM site, when my senior dog really started to slow down and gradually trialled different supplements. He was on Yumove for a couple of years, but I found it wasn’t that effective once his arthritis was more advanced.
If he’s in pain and not wanting to walk, there is a lot more your vet can do for him. First line vet meds are usually NSAIDs like Rimadyl and once they are established, vets have other options they can try in addition.
My boy is on Rimadyl twice a day, plus paracetamol three times a day, via the vets.
The supplements we settled on were Riaflex and Green Lipped Mussel from the same place, high strength Omega oil capsules and Healthspan Turmeric for Dogs. Interestingly, we saw the biggest improvement after a month to six weeks after introducing the Turmeric, but that could have been the combination of all the different things we introduced over the year.
CAM have just started offering an online owner course, to help people get fully informed about how they can help their arthritic dogs.