It’s not wrong to think about what you want or need for your viva. Better to focus first on what you already have to help you succeed.
You have a thesis.
You have experience.
You have regulations.
You have expectations.
You have examiners.
You have a supervisor.
You have colleagues.
You have friends.
You have talent – you must have this if your viva is coming up!
You have a lot to help you. Maybe you have doubts too, but you don’t want or need those. What are you going to use to work on beating them?