It's good news that they seem to have worked out what's wrong with you anyway, Susan. Let's hope that it will enable you to enjoy life more fully in the future. If you need any info/advice about your condition, this might be a good place to start:
https://www.kidney.org.uk/
I can understand the compulsion to keep drinking fluids when you've got kidney problems. When I went for 11 days without being able to pee (before being rushed into hospital with kidneys having the lowest level of function short of actual total failure), I was drinking water by the gallon - which probably wasn't such a good idea when there was nowhere for it to go!
Postcards or Kindle games? Now that must be a really hard decision to make. (If you opt for the postcards though, other AB members will be able to join in when you tell us about the obscure text and images that you're trying to classify!)
Whatever it is you choose, I hope that you enjoy your evening.