The problem with bringing a cat home as a trail, is you already have to take time to introduce a cat to another. Cat introductions can take anywhere from 1 week to a couple of months. You need to keep them in separate rooms, exchange bedding so they can get used to each others scents. It has to be done slowly. So it would almost be unfair to keep another cat for say a month, have them go through all of that and then if they don't get along in the end return the second cat.
If you decide on another cat, yes try to find one that would be a good fit, personality wise, and temperament wise, but it's a commitment.
It took me about about two weeks to introduce Vlad and Oksana to each other as kittens, and about a week to introduce Kiska and Maks to them. However it took me almost 6 months to introduce Czari to the others, so patience is the key.
I think Monkey would greatly benefit from having a companion.
There are only two rules at my house: House rule #1. Cats rule. House rule #2. See rule #1.