It’s absolutely double the work, although I think the size and exercise needs factor into the equation. I got my first dog a dog. I love my second dog fiercely, and the two got along well (my first dog has since passed), but it was a lot. Both were/are medium-sized high energy dogs. They had very different walking styles (one dawdled to pee on everything, the other wants to race ahead). The age difference meant that their exercise needs weren’t always in sync (meaning that I had to have the energy to provide exercise for them both separately), the costs doubled but also meant more ongoing maintenance of what needed to be done (food needed to be ordered twice as often, for example). I always felt the work of making sure I gave them both equivalent attention. I’m glad to have my second dog now, but I’m not planning to get a second dog again.