Hi Ellie,
Do you have any local animal hydrotherapists? Quite often they have tanks with a treadmill at the bottom that remove the weight bearing stress on your dogs joints so will allow them to exercise with minimal discomfort to the issues you've mentioned.
Alternatively you could find a river/body of water with easy access for your dog and concentrate your play here.
I would always recommend discussing exercise plans with your vet, voicing your concerns as they will be able to offer further support where necessary.
kind regards!