Why use polyester that is cheap and doesn't have a long lifespan?

Hello, I was directed to your comfort origins mattress using your questionnaire, however I was just wondering why you use polyester in your mattresses as I have also just read on your website that polyester is very cheap and does not have a long lifespan? The other mattress that was recommended for us is unfortunately a bit too expensive for our budget. Is there anything inbetween?
Regards,

Lisa