I'm so sorry for your loss. I'd be very careful about getting another cat, there's no guarantee that they would get on at all. And it's very unlikely that they would bond and provide comfort to each other. That usually only comes with littermates, who've been together since birth, I believe. We have a mother and son pair, inseparable until he was about six months old (to the point that the rescue insisted that they be rehomed together, wouldn't consider separating them). Then he spent a day at the vets being neutered, came back after eight hours smelling 'wrong', and she's disliked him ever since! They tolerate each other well, but they're never found snuggled together. There are frequent displays of annoyance - chasing, hissing, swiping. And that's from a pair who WERE bonded for a while.
Leaving your remaining cat home alone, with a trusted cat sitter, is going to be far less risky than leaving your remaining cat home alone with a new, strange cat. He will be OK.
Maybe others will be along to say that they've had an old cat and a new cat bond beautifully, but it's never been my experience (and I've had eight cats so far in my life).
You MIGHT do OK with a new, young kitten - older cats often accept a kitten better than a new adult cat. But would you want to be leaving a kitten to go on holiday in a couple of months' time?
Remember also that animals live much more in the moment than we do. I'm sure your cat is missing his brother a lot right now, but that will pass surprisingly quickly. By May, he probably won't remember that he ever had a companion cat. One of our cats went missing for five days a couple of years ago. When she returned home, our other cat had clearly forgotten her entirely! It took a few days for them to settle together again. (Come to think of it, their relationship - already strained when she went missing - has been worse since that brief separation and reintroduction.)