Hi jwiley1017,
I’m sorry you’ve had some bad luck with your recent mattress purchases, either through poorer quality materials or comforts that don’t fit your personal preference or (newer) sleeping position.
Unfortunately, there is no general consensus (nor would it be possible) of universally applicable comfort designations like “medium soft”, but the term is of course important as it relates to you and your ability to compare one item to another. Also, pillow top isn’t a designation of comfort, but rather a description of mattress construction.
I think from what you’ve described is that you desire something that has a “plush” surface comfort, but not so soft that you sink too deeply into the product, but also not so firm that it is uncomfortable to you when sleeping upon your side. Sleeping directly upon the foam, you like something that doesn’t have a polyfoam quilt panel on top. The Serta mattress you mentioned you tried in a showroom is a memory foam product, and would tend to have a bit more of a "dead’ feel to it than a “springy” feel.
As you currently have all of the layers of the 12-1 mattress (they are all good quality 2 lb. polyfoam pieces), your idea certainly sounds like the beginning of a fun DIY project.
I would recommend holding off on a mattress cover at first, as you may end up experimenting with different configurations. Besides starting with your initially expressed configuration (firm poly foam, medium polyfoam, latex), you may desire a bit more surface plushness and also end up also experimenting with using all three of the polyfoam layers with the latex on top (perhaps something like a firm polyfoam, medium polyfoam, plush polyfoam and latex; or firm polyfoam, plush polyfoam, medium polyfoam and latex) and end up with a thicker product. You might even desire a bit more of the “springy” latex feel and decide to do something like a firm polyfoam, medium polyfoam, medium latex plush latex. Once you come up with a final configuration, I’d then pursue a mattress cover – preferably one that is a stretch knit to not inhibit the feel that you’re attempting to achieve and what you stated you desire.
As you are attracted to the idea of designing and building your own DIY mattress out of separate components that are purchased from one or several different sources then the first place I would start is by reading option 3 in post #15 here and the posts it links to (and option #1 and #2 as well) so that you have more realistic expectations and that you are comfortable with the learning curve, uncertainty, trial and error, or in some cases the higher costs that may be involved in the DIY process. While it can certainly be a rewarding project … the best approach to a DIY mattress is a “spirit of adventure” where what you learn and the satisfaction that comes from the process itself is more important than any cost savings you may realize (which may or may not happen).
I’m looking forward to what you decide to do and your results.
Phoenix
Note Added: I forgot to address any potential quality retailers in your area that might offer latex. I did a search and the closest I found were quite a distance from your home. I couldn’t find anything compatible in Watertown, Brookings or Aberdeen.
Subject to confirming that any retailer or manufacturer on the list that you wish to visit is completely transparent (see this article ) and to making sure that any mattress you are considering meets the quality/value guidelines here … the better options or possibilities I’m aware of in and around the Sioux Falls area are listed in posts #2 and #3 here . The better options or possibilities I’m aware of in and around the Minneapolis/St Paul area are listed in post #2 here .