This is something i do still now if i feel too tired to make the bed and dh would never have bedding on if i didn't make it (he'd sleep in his sleeping bag on the bed or even on the floor quite happily).
I know it's not the MN view, but i never understood parents angst about what their children do in/with their rooms. I suppose it depends on how you see their room and the furniture in it, do you consider it to be theirs or do you think you are letting them use your stuff till they leave? It just seems so controlling to me.
As someone who grew up being reminded i was living in someone elses house and not paying my way, i felt incredibly frustrated and not really welcome. I think this view is unfair - as a teen (i left at 16) you can't contribute or purchase your own bed etc. Therefore you never really feel like that is yours or that you have control over even small aspects of your life. Personally i never want my children to think they are lodgers in their own home.
However, i think there is something very different between not making your own bed in your own personal space and not contributing round the house - the not helping with the bag is outrageously unkind rather than lazy - if my ds was that uncaring towards me i think i may cry.
If it were me i would defo address the not pulling weight communally and the unkindness, but i would leave him to his mattress quite happily. I would also not do the laundry for him either at that age - if he wants to live the way he wants then let him. Let him be more independent and don't worry what he does with his bedding.
Out of interest, (genuine question) how does sleeping on the bare mattress ruin it?