Honestly, the fact that you won’t have enough time for your single cat is the best reason to get them a friend. Of course if you have the funds to take care of the second one as well. This is how I ended up with my second one.
I work 8 hour days and once I took 1 week holiday abroad when I had only one cat. I hired a sitter to come check on him twice a day and play. I also have pet cams around my apartment and he seemed sooo lonely and sad the whole time i was gone. Seeing him like that, i was crying during our trip. My boyfriend took me to the shelter as soon as we came back.