Had lots of experience with horses and arthritis. No idea if any translates to dogs though.
With one of our horses, the regular injections stopped working after a while. We fed him supplements and let him have the day off when he was on a bad day. All told, we kept him in light work for 11 years after diagnosis. The critical thing is regular exercise when he is up to it.
We used to use Cortaflex on our horses. IIRC, they have one for dogs. It is expensive, so a standard Glucosamine for dogs could be a better bet.
Take a look here:
https://www.equine-america.co.uk/collections/cortaflex-for-dogs - check the ingredients and you should find a much cheaper alternative. We have changed over to a standard Glucosamine supplement which seems to do the same job on our horses and is a fraction of the cost.
We also use cider vinegar as a feed supplement - it has the advantage of being cheap if it doesn't work. A quick search found lots of references to it being used on dogs.
The biggest problem you could have is that you will end up giving Archie several supplements - but you won't know which one is working. You will therefore be unable to stop feeding any of them "just in case".
As with all things feed supplement - check for a solid reference re dosage and introduce into Archie's feed gradually. That way you will have less chance of him turning his nose up. And, in the extremely unlikely event of any adverse reaction, you will have only fed a small dose.
In the horse world, there are some natural pain killers which help too - I don't know enough about dogs to recommend one.
