Hi Ruth44,
The first suggestion I would have is to start with the tutorial post here which has all the basic information, steps, and guidelines you will need to make the best possible choices … and know how and why to avoid the worst ones which would include the major brands such as Serta or any mattress where you aren’t able to find out the quality of the materials inside it.
The weak link of a mattress is almost always in the use of low quality materials in the comfort layers and if you don’t know the specifics of what is inside your mattress you have no way to identify any weak links in the mattress or make meaningful comparisons with other mattresses so you would be making a completely “blind” purchase much like the hotel mattress you purchased (you can read more about hotel mattresses in post #3 here).
I would completely change the way you are looking for a mattress and if you follow the steps in the tutorial post one by one you will have much higher odds of success.
Phoenix