i have used this stuff occasionally with various cats. some hated it, but some love it. it can be given as a treat or mixed in their food
https://www.amazon.com/dp/B000RI3ZG6/ref=cm_sw_r_cp_apa_fabc_KNXSFbQ9SHWZ4
Aww I love this question. My cat is 17 and in the past couple years, I've gotten her more expensive things that I'd had on my wish list for awhile. One was a bird feeder (plus a shepherd's hook to hang it from) to put in the backyard so she could watch birds. That has worked out really well, especially as it attracts furry critters who pick up the mess on the ground, and she loves watching them, too.
Secondly, I got her this actual cat tree although she didn't take to it as much as I thought she would. I know you said your kitty has arthritis so I don't know how much jumping she does, but the tree platform isn't very tall.
I've been mixing a crushed pill into one of these squeeze-up treats for my girl. I switch between flavors. She wouldn't even touch a pill pocket. https://www.chewy.com/hartz-delectables-squeeze-ups-tuna/dp/358272
Maybe he’d prefer a brush like this It’s rubbery and soft, kinda gives them a massage.
So the one in the picture is just one we found on Amazon when we searched for heated beds. Her favorite one (not pictured) is a K&H Thermo-Kitty bed. I'm pretty sure you can get them on both Amazon and Chewy. Thermo-Kitty Bed
I was just about to say this is what I do when I won’t be home, or for the meal my kitty eats overnight. It works pretty well.
OP, you can even freeze a meal-size portion of food and put it in the feeder if you won’t be home for awhile.
Catnip Banana!
Our blind 20 year old boy loves to roll around and rub his head on this banana. The other two cats are crazy about it, too! We've bought 3 of these in the past year. Hope the link worked. (Otherwise google cat banana:) https://www.chewy.com/yeowww-catnip-yellow-banana-cat-toy/dp/130264?utm_source=google-product&utm_medium=cpc&utm_campaign=hg&utm_content=Yeowww%21&utm_term=&gclid=Cj0KCQiA5OuNBhCRARIsACgaiqX5sV6XwzrHnSk9AsiVCqQ9SzlfST30eSxpYdC70mhP-omM4SBd6QMaAtyfEALw_wcB
It's a constant struggle. Good luck! I thought I would also mention: sometimes just changing my kitty's bowl sparks interest. I move it around the room, and alternate with an elevated bowl. Kidney disease is associated with excess stomach acid, so sometimes they prefer to eat from an elevated bowl (gravity causes acid reflux when they lower their heads).