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,

I just bought an serta iseries jubilance. It is too early to give a full evaluation of it - need a few weeks.  But I can tell you I would not recommend the applause cushion firm model in the iseries or any of the lower priced iseries models (the ones with two stripes). These cheaper iseries models make use of various forms of polyfoams, which I do not like for their longevity. 

You should take a look at the three top iseries perfect day models (they have one stripe).  These three top end models use only memory foam(s) over the new duet individual pocketed coils. They have no cheap  polyfoams. Polyfoams typically result in the sagging issues as they deform quickly with wear.

The iseries gel foam is 4lb 10.5 IFD (average quality memory foam).  The two top models also add the higher quality 5lb koolcomfort foam (good quality open cell memory foam) on the top layer, which was one of the reasons I chose the Jublianace.  You could also consider the very firm iseries Enjoyment model and possibly add a latex topper to soften it a bit.