I bought a tall box from Amazon made by IRIS.

if the cat doesn't mind it. My late cat Pixie used to hang her butt outside the box when she peed sometimes, like she didn't really know where her butt was; and getting a large, higher-sided box mostly assured that she'd get all of herself in the box before she let loose.

I have a pretty big kitty..15 pounds so I got the largest one and she can move around in it but it’s not real deep so she gets in n out easily. Also, I don’t have it covered..I don’t think cats like being confined plus it’s a lot easier for me to keep clean with unscented clumping litter. 😸

... I catch him running I go and bag the poop and any pee balls. He wants his box clean, like after every use. The better I am at keeping up with the box, the less likely he misses the box. A great cat who is the cleanest clean freak I've ever known. He bathes him self continually.

I got a dog crate pan to put it in: https://www.chewy.com/midwest-lifestages-dog-crate/dp/102280. Even though that cat is gone, I now have two of them - it helps contain the litter somewhat.

A cat that isn't used to a lidded box may not switch easily to one. Taller sides is also good.

They're available from Home Depot for about $17. The bottom corners have enough curve to be easy to scoop the litter.
I have four cats, so the size helps avoid misses. I don't think a covered box would be big enough for a couple of my cats as they are rather large. Your Holly might be fine with a covered litter box if she's small enough to turn around in it.

as the stainless does not hold odors. Mine has one lower side for the cat entry, and we never worry about the accidental tinkle outside the box now.

claustrophobic. I've only ever used a large open box and softer litter.

I own a cat boarding business. Instead of litter boxes, I use for my boarders AND my own cats...18 gallon or larger Rubbermaid containers and cut a large opening for the cats. They can stand up move around without being cramped and Yu can use a lid or not. I have always felt bigger and taller is better. Especially for sprayers.

We're down to one indoor cat now, but I've never had a cat with a problem jumping in/out of one.

box, without the lid, and cut a hole starting about 5 inches from the bottom. It worked great for us... and them.

The plastic storage box was too flimsy and bulky to clean and empty by itself, and was easy to clean when they missed. Put a small amount of litter at the back and front to catch mistakes. Vet said some cats hate covered litter boxes and it can compound the problem. Some cats also like to see what's going on around them when they use the litter box. This worked for all of our cats. Good luck!

50+ years of marriage. We have used different strategies depending on the cat. We have used a big heavy, sturdy grey storage tubs, (with out the lids) if the cat was able to jump into the storage tub. We have also turned a bathroom bathtub, plugging the drain, tarps lining the tub and duct taped into place, so it wouldn't mess up our plumbing. Both systems have worked for cats who missed the litter box. Their age, health and if they were born feral can affect their litter box usage. All of our cats were rescues, thank goodness for clumping litter. We now have one 16 year cat (feral) who uses her automatic litter maid cat box, with no problem. Her sister, who passed 2 years ago, wouldn't go near it. Both rescued from the gutter, just barely able to crawl, eyes barely opened. Daily cleaning of their box helps, because they don't want to step on their poop or pee to go potty. Good luck.

Whichever way you go. None of my cats have liked the covered ones. Maybe if made from clear plastic. You can always get a big storage container and cut the entry area into it. Put the lid on or off either way it would be nice and tall.

Either way maybe you should put one of those puppy pads for house training under the pan so that the edges around the sides of the pan catch any pee and it doesn't stain the floor.

You can buy sheets of acrylic at most home improvement stores. I've used them against the wall where a cat was peeing. I have had older cats that just weren't always reliable in the box.

This keeps the urine from getting into the wall (i.e., drywall material, etc.) and makes it easier to clean up and keep from smelling.

Again, this is something that might help, but won't solve the problem with the kitty, obviously.