Hi Steve, The memory foam overlay has a three year manufacturers warranty and normally it is probably 5 plus years before any noticeable softening occurs and you would begin to think about replacement i would guess. It just comes in a stockingette cover but a 70% cotton, 30% polyester cover can be purchased seperately for $40 for single, $50 for double, $60 for Queen and $70 for a king. We recommend using a protector of some sort for all overlays to help keep them clean and in good condition. Freight can all be calculted using the online calculator.