Hi Annie!
If this is new to you, I would suggest worsted weight to start with, and then eventually category 3 (sport weight yarn). Remember to size down your hook about 2mm from what you would normally use! I have a beginner guide here that might help you: https://littleworldofwhimsy.com/my-foolproof-guide-to-crocheting-amigurumi-for-beginners/

Best of luck!