My kids have had much better formal training in swimming than I did, and swim at school. It's a great skill to have. My daughter was going to join the swim team before...

and I keep agonising over whether swimming indoors is a selfish and unnecessary risk

Purely my opinion of course, grain of salt, etc. etc. but I don't think it is; exercise is so important for mental health. And as you said, the numbers are very low where you are. Perhaps you could try it out once, maybe even a quick change into dry clothes but no shower, and see how it makes you feel?