In Buddhism there are six levels of heavens in the 31 different realms . These are ranged from the lowest heaven up to the highest heaven . Then , what is Nirvana ? , Is Nirvana the seventh heaven ? The ultimate heaven ? Is Nirvana the 32 th realm ? . If there are so many pleasures and happiness in the 6 heavens (in the 31 realms) , then what kind of pleasures and happiness we will find in Nirvana ?
For any realm one can abide and say, "I am here." Not so Nibbana/Nirvana, which is the cessation of identity view.
MN1:124-146.23: nibbānaṃ nibbānato abhijānāti; ...
MN1:124-146.23: They directly know extinguishment as extinguishment. But they don’t identify with extinguishment, they don’t identify regarding extinguishment, they don’t identify as extinguishment, they don’t identify that ‘extinguishment is mine’, they don’t take pleasure in extinguishment
In a sense yes nirvana is the 7th heaven, but it is beyond the realms of form and formless. Nirvana only comes after you have overcomed 6 realm.
The other point you talked about 31 different realm within those 6. All suttas have talked about it, but according to my experience it is 32 different realms and adding nirvana to it, it becomes total 33 realm. Also, this is true when we compare it to our number of vertebra. We all have 33 vertebra. But don't take my words seriously until you experience it by yourself.