Cat won’t stop meowing. Is he lonely?

Hello I got my first cat about a year ago. He was a stray I was feeding in my last apartment, I was just feeding him for a few months and one day he followed me into the apartment and basically never left. I got him neutered, all his vaccinations, and treated for mange and the vet didn’t say anything about whether he had been in a home previously but he is the nicest cat in the entire world, so I can’t say for certain if he lived his whole life on the street. The vet also told me he was 2 but after taking him to another vet they said he was at least 6, so I’m also not too sure how old he is.

Anyway my issue is that I moved into a new place and started another job on top of being in college, I am home for about 6 hours of the day to be with him but I now it’s not enough, he’s recently started meowing non stop whenever he isn’t eating or i’m actively petting or playing with him.

After searching through other threads I want to get him a friend so he isn’t lonely throughout the day. I wanted to know if it’s a. realistic to get another cat when I’d hardly be here to monitor them/introduce them, it would have to be done within a few days, I can keep them separate so that’s not an issue. b. what kind of cat would best suit him? He’s definitely on the older side and the only other cat I’ve seen him interact with was a kitten at the old apartment, I feed them both one time and he would hiss at the kitten whenever he tried to eat his food but beyond that he was fine with him.

side note: he went to the vet last week where I was informed he has dental disease and has to have several teeth extracted, with is upward of $900. I definitely plan on doing it in the future but the vet informed me that as long as he’s eating fine he isn’t in any active pain. I thought that may be the cause of all the meowing.