Thank everyone who's helped. I've reached out to UEFA who have said the reason there was no accessibility seats listed is because I need to upload proof of eligibility before they'll become visible - so I'm currently trying to get some sort of letter at short notice from the hospital to see if I can grab one of these tickets.
So will see how that goes in the next few hours. Here's hoping!
Thanks to everyone offering to help me out (I've received quite a few PMs!). Unfortunately there's not really anything anyone else can do - I can climb stairs by myself no problem so long as it's just a few of them, but it'd be too tiring to climb to the upper tiers. I'm hoping UEFA pull through for me on this one.
If not I might decide to roll the dice anyway as said and hope I either get a seat lower down or there's some internal elevator etc. They seem to have opened some cat 2 restricted view tickets online today at 55 euros so I could probably just take the chance at that price considering it's a once in a lifetime thing and hope it works out (120 would sting though if it went bad!)
EDIT: get in they accepted the proof! Got one of the easy-access tickets for 30 euros, absolutely buzzing!