So sorry to hear about Scrappy having arthritis so young.
My old girl has arthritis in both her back legs after having cruciate ligament opperations on both, and has just started developing arthritis in her elbows in the front legs.
I do find exercise wise swimming is great for her as it takes the pressure off the joints as the water is supporting her weight and still gives her enough of a work out to make her tired.
My girl is on Glucosamine tablets every day since the arthritis has started in her elbows and it seems to help a bit but no great miracles.
I have found that my girl likes to be able to stretch out when she sleeps and not have her legs tucked up underneath her. Must have something to do with getting the weight and pressure off the joints again. She has her own three seater couch but is only on it occasionally as it just doesn't have the room for her. She has a dog bed on the floor during the day and at night now sleeps on a queen sized bed. It's just the guest bed and i never have any guests so she may as well make use of it.
As you've already mentioned keeping them off hard cold concrete floors and keeping their weight down also helps greatly.
If you think dogs can't count, try putting three dog biscuits in your pocket and then giving Fido only two of them. ~Phil Pastoret