Thank you for the enormous input. I used all the info I got from you all to goreng the selesman at the gallary hahaha.

So far I've tried

Normal foam - cheopo soft. I think not good for the spine. Won't last long obviously.
Latex - Comfortable, soft, but did not 'force' my posutre to a correct one imo.
'High-density foam spring' - Quite expensive than the others. Comfortable like hotel one. For spine wise, hmm so-so i guess.
Coconut fibre - Wow..... hard like lying on the floor. I can see myself to get used to it, but at the moment....wow...dem hard hahaha. The pro is my spine is 'forced' to be on a correct position.
High density foam - This is best of both world. Stiff enough to make my spine into correct position, but not that hard like lying on the floor.

I think its either coconut fibre or high density foam. Both from the Mastercoil brand. Just need some time to rethink 

*btw I am a 100% back sleeper.