I want to hear more about stitching your own mattress back home
Why isn't it possible in USA?
The way it is done is you take an old beaten unshapely glob of a mattress made of cotton to these small retail stores/factories in your neighbourhood. They cut the outer layer open and remove the cotton. They segregate the good fibres and bad ones and about 70-80% of the mattress is still reusable even in a worn out mattress. They are able to do this rather easily since the cotton has laid out in the form of lattices(think of squares in a game of tic-tac-toe) with stitching. They remove the stitching and discard the bad lattices(basically the areas that have been heavily compressed like the ones in contact with your butt or hips). After adding the new cotton, they recompress the whole structure and then add stitching back to recreate the lattices. Finally, they add a mattress cover over this cotton.
This way mattress gets reused and no buys new ones. They may add coconut or jute fibre to make it stiffer if you want a change in the firmness. Any bed bugs, dirt and grime if present is only in the outer layer and if you carefully remove it the cotton beneath is still safe.
I've slept for 5 years on a mattress whose cotton came from a bed my great-grandmother slept on. The cost of this whole thing is about 5$ and you do it once every 10 years or so.
You help out in the store by helping them cut the stitching, add the cover, etc.
I feel it isn't possible in America because there are no small/independent businesses who will work with you and help you do it.