We are looking at a therapedic mattress. it has a 3" talalay yop with an 8" polyeurathane core. any opinions on this? we have a simmons world class super plush pillow top king that is going to be ruturned under warranty because it is sagging 2" in the areas where we sleep. the store is being very cooperative with us and gave us a credit for the simmons but all they carry other than simmons is therapedic. we have read a lot about latex and think we will be happy with it but we are concerned about the poly core. don't want to make another mistake & have more mattress problems. any info on this would be greatly appreciated. thank you, looty