Formal:
* برای من دنیا را عوض میکند: (barāye man donyā rā e'vaz mikonad) - This literally translates to "it changes the world for me". It's a more poetic and elevated way of saying it.
Informal:
* خیلی برام مهمه: (kheyli barām moheme) - This means "it's very important to me". It's a more casual and straightforward way of saying it.
* خیلی دوسش دارم: (kheyli dūshesh dāram) - This means "I love it very much". This is a very strong and affectionate way of saying it.
More specific options:
* مثل جونم برام مهمه: (mesle jūnam barām moheme) - This means "it's as important to me as my life". This is a very strong and emotional way of saying it.
* بدون اون نمیتونم زندگی کنم: (bedūn ūn nemītonam zendegi konam) - This means "I can't live without it". This is a very strong and dramatic way of saying it.
Ultimately, the best way to say "mean the world to" in Farsi depends on the specific situation and the relationship between the speaker and the listener.