Sorry to read about the headache, ajn. I had one for a while not long ago after my Covid jab, so I know how rotten they can be. {{ajn}}
Nature’s Feast ‘No Mess’ is the best bird seed I’ve found. It lives up to it’s name because it doesn’t contain any cheap ‘filler’ seeds that don’t get eaten. Unfortunately it’s ridiculously expensive and always seems to get ‘Lost in Transit’ when I order from Amazon (i.e. ‘Drop Shipping’ – They take your money and tell you it’s Dispatched without checking that the Mother Ship warehouse has any In Stock first. When it doesn’t turn up they swear blind they sent it and claim it must have been ‘Lost’). These days I use Peckish Complete ‘Seed and Nut No Mess’, which isn’t as good but is good enough – and actually arrives!
Don’t worry about the mouse, though. Where there is one mouse there are more mice. It is the nature of mice.
I feel a lot more sorry for the now-homeless, friendless and unfed cat. Maybe you could let the RSPCA know it’s around so it can get caught before it gets fleas, ticks and FIV? My sister always takes in rescued cats – the last had been savaged by a dog and her current one lived rough for 8 months and now has FIV from fighting other cats and only can only go outside on a harness.