boho43, you're doing the exact right thing keeping yourself and husband in self isolation despite not having the virus... Both being octogenarians and both having cancer you need to protect yourself from other people.., that's simply the most important thing.,.
While you're well you needn't hole up in the house necessarily but if you live near a large country park or woods then perhaps you can get out for a walk, or even a drive to somewhere.. but stay at least 6 feet away from any other person, in a store or anywhere that you may have to be where there are others. I hope you have enough stocks in or can get someone to do it for you to last if you do get poorly...and can't leave the house, but do remember that you are still permitted to use your garden. However if only one of you contracts the virus then only one person can be out in the garden on their own.
Good luck to you, you have enough to contend with without the worry of contracting this Covid-19, and that's the same for all of you with underlying health issues and who are especially at risk.