u/Happy-Armadillo-120

My family has rented a summer cottage for 2 weeks for the past 2 years and will be again in August. The owner, a lovely woman in her 80s, lives next door. The mattresses have got to be 40 years old and are torturous to sleep on. Can I/how can I offer to buy a mattress (that she could keep) without offending or confusing her?