I also live alone and have fatigue/pain issues, so I know your pain.
I usually try to Hoover my floors once a week, but I don't have any pets. You may have to accept there is hay around sometimes, I mean it's not dirt is it? Though I've seen you've asked about a robot Hoover in another thread, so that could be an idea worth considering.
My advice as far as the sink and bath is concerned (especially the sink if you're saying it gets dirty fast) is to have a small towel specifically for drying them out and try to do it once a day, or just after using the bath. I wipe my sink out every night before bed, it only takes a few minutes and really helps keep it clean. If you use the bath often and wiping it every time is too much, maybe every few times? To help keep actually in the toilet clean I have one of those sticky smelly things stuck on the side of the bowl that get activated every time is flushed, they last about 3 weeks usually. Obviously it still needs cleaning properly, it just helps make it less of a big job. As far as stuff collecting, would it gross you out if it did it a bit more often before it gets so bad?
In general I really find doing small things as in going makes everything seem like less if a huge job when it comes to the proper clean. Maybe to help with motivation you could try to set routine days when you do certain things? One thing I always try to keep in mind though it's pacing and not doing things if I'm really not feeling up to it even if it's when I should be doing, I know I'll only end up paying for it after.
I hope some of this has been helpful and you find some ways to figure out your cleaning!