iPhone storage (Capacity between 128 of 7plus and 128 of 12promax

I’m currently using 7plus with 128GB and used storage is 89GB then i would to buy a new iPhone 12promax with 128GB my question is whether 89GB will be transfered to 12promax and i will only have 39GB left for using in my new 12promax ? Need your suggestion which capacity do i need to select for 12promax like between 128 and 256 base on my current capacity of 7plus. Thank you