Hello, I almost bought a Heavenly bed when I tested a Serta iSeries Applause Cushion Firm bed. They both felt very good. I read some reviews for the Heavenly mattress and many reported sagging of the mattress. I couldn't find reviews for the Serta mattress. not sure if it is a brand new model. Can anyone help with comparison between these two mattresses and maybe suggestions? Has anyone bought the Serta iSeries? Thanks,