It is very common for people to use more than one bullet journal per year. Me personally, I used two bullet journals last year. Other people manage to use only one, but I've also heard of others that use 3 per year, or even more! It all depends on how busy you are, and how many spreads you create in your bullet journal.
No matter how many bullet journals you use per year though, there'll come a point where you'll need to move to a new notebook eventually. And that can feel a bit daunting for some, especially if it's the first time you're doing it. But don't worry. There are certain steps you need to take to make this procedure as simple as possible.