Radar update:
Hydration levels still not where they should be, URI a little worse - the prognosis is still excellent, they're just being cautious. So keeping him in tonight and quite probably tomorrow night as well, depending upon how he progresses. He is at least accepting the feeding tube* fine, so once the other issues are improved, he will be able to come home.
I wasn't able to visit today unfortunately - I'd go every day but I don't drive and it's a 3 hour round trip by bus, so with my mobility issues/arthritis it simply isn't feasible for me to visit every single day - I feel really guilty about that tbh
I want to stress that he is very happy in himself, in good spirits. Although he's clearly delighted to see me when I am able to visit, he's a brave and curious cat, and has never been that disturbed by new situations and new people - so he adjusted to being in hospital really quickly and is quite settled in there, and he's not afraid of being handled by the vets and nurses even if that involves him being poked and prodded sometimes - he is climbing into their arms for cuddles when they are tube feeding him for example.
So he's not undergoing any undue stress or misery or pain - he's just feeling a little poorly. Would hate anyone to think that our decision to use a feeding tube was cruel or anything, he's happy despite his stay in hospital and the tube, and will have a good quality of life at home even if it takes him a few weeks to start eating by himself again.
*The feeding tube is an oesophagostomy tube, it is very narrow, and enters through a tiny hole (stoma) in the neck and goes down the oesophagus - it doesn't go through the nose which isn't so easily tolerated. Cats are still able to drink and eat by themselves with this sort of tube fitted, the tube is used to deliver a liquid food if they are not eating post-surgery or during illness, or to top up if they are eating less than required. Once they are back eating, removing the tube is a very simple process that doesn't require surgery or anaesthetic, and the hole heals up. In case anyone wondered what I was talking about.