The mattress is very uncomfortable.
ma-te-RAS-so — four syllables, stress on the third. Double 's' is slightly longer.
Mention this at the front desk — an uncomfortable mattress is grounds for requesting a room change.
'Scomodo' (uncomfortable) is the opposite of 'comodo' (comfortable). The prefix 's-' creates a negative in Italian: 'comodo → scomodo', 'fortunato → sfortunato'. 'Materasso' = mattress. Comfort in Italian hotels varies enormously by price and category.
Il cuscino è troppo basso/alto.
The pillow is too low/high.
Specify your pillow preference — hotels often have alternatives
Il letto scricchiola.
The bed creaks.
A creaking bed frame can seriously disrupt sleep — report it
Posso avere un cuscino diverso?
Can I have a different pillow?
Many hotels have a 'pillow menu' with different firmness options
Italian hotels are not legally required to change mattresses on a fixed schedule. Older budget hotels sometimes have mattresses that have seen better days. If sleep quality matters, choosing a 4-star or higher hotel is the most reliable way to ensure good bedding.