I'd just move the old box upstairs for him and buy another one like it for the other cats. Also give them the new covered box. Replacing the original box should help keep your other cats from getting upset that their box was moved upstairs.

You can put a latex backed rug under the box upstairs to catch anything that goes over the edges. If he has trouble getting in it, I also wouldn't hesitate to take a knife to it in order to make access for him easier.

It's just part of having a geriatric pet. We have to make accommodations and just live with the changes.

There's one out with mini stairs- it's huge and dome shaped, he might like it better.

I am not a fan of covered litter boxes. Cats just don't seem to like them, and they are hard to scoop daily. If a cat is bullied by another cat while in a covered box, they have no safe exit and that can lead to serious litter box aversion/problems.

Our sweetie, Asia (who we put to sleep a month ago at 17) had problems hanging her backside over the litter box, onto the floor, instead of into the box. What I did was put the litter boxes on larger metal trays & I kept paper towels and spray cleaner & water to clean up when that happened, maybe a couple times a week. DH is a steelworker, he made them for me. They are basically giant cookie pans. I've seen plastic trays that I thought would work in stores also. I scoop daily and we never have odor. I usually scoop into sandwich bags, then seal and toss. My version of a diaper genie, lol.

As cats age their kidneys often fail, and they drink and pee a lot more to compensate for that. So as your cat ages and has trouble with the stairs, he needs a viable litter box on the level he spends most time in. And you definitely don't want odor or your floors ruined.

I posted a link to something similar to what I use, it is for food, but would work for a small litter box & you can wipe it as needed. With the raised sides, urine wouldn't leak onto the floor.

Good luck with your cats!

Here is a link that might be useful: food tray

OH HAPPY DAY!! I have good news - he has used the new covered box!!! Actually I have two new covered boxes - one is the big round dome with the little stairs that go inside to the litter area. The other one is a smaller regular covered one and I have put that out in the screen porch where he spends all day. I put him in the one on the porch today and he dug around and did #2. Then he came into my study a little while later - where I was on the computer - and went into the dome and did #1. Yippee!! Who would think one could get so excited about a cat using a litter box....only a cat lover could appreciate this.

Someone is also going downstairs so I'm still hoping the other cats just carry on as usual with that.

thats great!

And yes only a cat lover could get so excited over a cat using his letter pan properly!

Well it seems everyone now likes the dome litter box! It's getting a lot of use which isn't ideal since it's not very big. Also old frail cat who really needs this box likes pristine clean litter which creates a new challenge. Three big boxes downstairs - one medium size upstairs. It's been so hot we've had the AC on so no one is going out on the porch. At least the dome is in a convenient location for continuous cleaning - when I'm home.

Next challenge - four level weekend lake place. I just stocked up on more litter boxes...... There are many people who would think I'm crazy.

Oh Gibby, anyone that loves cats would never think you're crazy...and if they don't love cats then who cares! LOL
I'm glad your older boy is comfortable with the covered boxes.