Grief therapy update: Improvement!

Jack

I have a cat named Jack. He's lived with me his entire life, from the time he was born, which was a pretty long time ago. Honestly, I don't remember the exact year but it was the late 90's. He means a lot to me. He's my furry, four-legged life partner.
My ex-wife and I were able to keep the whole family together when his mother gave birth to Jack and his two sisters in our living room back in Sarasota. They all came with me when I was on my own.
His mom and one of his sisters passed away a few years ago, so it was me, Jack and his sister Macy together since just before we all moved into my house.
About two weeks, ago, we lost Macy. I came home from work and she had apparently died in her sleep. Jack was lying right next to her.
Over the next few days, Jack was very lethargic. He'd crawl under the bed covers and spend the whole day sleeping. He stopped eating and lost a pretty dramatic amount of weight in a very short period of time. It took me a few days to really notice but eventually it occurred to me, "I recognize this behavior; the poor little guy is depressed!"

This is Macy and no, I'm not good at selfies with cats.

Well, of course he's depressed. I did the calculation and he never spent as much as a whole day separated from his sister. Now he's the last one left from his family and plus, with my goofy schedule, he's all alone all day long. Even when I'm there, it's just me.

Pictured: Consolation prize

I implemented a grief therapy program of my own design, consisting mostly of really good food and extra intense snuggle time complete with heavy duty petting and the cooing of sweet, sweet baby talk. That's what I would want if I were grieving.
The root element of this therapy consisted of opening a can of Fancy Feast cat food (Classic Savory Salmon flavor) and bringing it into the bedroom. As expected, he was under the covers sleeping. I woke him gently and got a mumbled meow that sounded like "Murph." I sat on the side of the bed with the bowl of food and started talking to him. He picked up the scent of the food and I got a "Murph?". He crawled out from under the covers and climbed up on my lap and started eating. I pet him and sat there patiently while he ate. He got down just over a quarter of it over about a half hour. We went to bed and he fell asleep, purring, on my chest. I set the alarm for a half hour earlier than usual and spent that extra time the next morning just petting and talking to him.
Next day, same thing (Classic Turkey and Giblets). And the day after that (Flaked Fish and Shrimp Feast). He comes out from under the covers on his own now and is eating a little more food each time. Last night, he got within a couple of bites of eating the whole can (Classic Tender beef and Chicken Feast). I can tell he's putting on and keeping some weight too. He still sleeps all day under the covers, which concerns me, but his demeanor is better when I'm around so there is some marked improvement. My schedule is still pretty hectic and I'm often not home until late and so I'm wondering if it would be a good idea to get him a playmate to keep him company during the day, but I don't know if it's a good idea. On the one hand, the merits are pretty self-evident. On the other hand, at his age, how will he take to a new cat? As much as he seems to be enjoying the attention, I don't know how he would take to having to share any of that. Should I get an older cat or a kitten? A male or a female? What about a dog?
If there's anybody out there reading this who has been through anything similar and has advice, I'd love to hear it.
In the meantime, tonight is Classic Tender Liver and Chicken.