Well, luckily, drifloon are fairly easy to care for, as most ghost-types are. They only require food, water, a place to relieve themselves, and entertainment. You’ve already taken care of the entertainment with your sylveon (although it wouldn’t hurt to purchase other light items for drifloon to pick up and play with, especially crinkling pet toys); the rest is otherwise easy. Drifloon are omnivorous (contrary to popular belief) but can be fed kibble if you don’t wish to feed them fresh food. They can also relieve themselves outside, but be sure to keep them on a leash tied around one of their strings to prevent them from being blown away in the wind.
In fact, that’s honestly the only challenge to keeping a drifloon: their tendency to blow away if outside. Generally speaking, drifloon can be taught through strength training (that is, training involving tying weights to its strings and having it lift them to develop their flight muscles) to increase their own weight and stay in one place, but until then, it’s imperative that you or your sylveon keep a tight hold on one of its strings.
Best of luck, anonymous!