Mark all that you can do for Clapton is take each day as it comes, I know this is hard and is how I have been living the past 19 months with one of my cats. All you can do is way up if Clapton has a good quality of life ie playing, eating, alert, etc, of course I do not include loved as we all know our animals are loved.
Some vets do a free weight check where you can just take them in and have them weighed, it is not ideal with a nervous cat but even if it is monthly it is better than guessing by just picking them up in your arms.