Hi jmatic,
I would certainly avoid the myside mattress because it is such poor value. There are many local manufacturers who will also do a side to side “split” construction using higher quality and known materials at a much lower cost.
The Simmons Beautyrest NXG line has some nice mattresses and I particularly like the feel of some latex and memory foam hybrid layering but here again the value is not good when compared with mattresses that use similar or even higher quality materials at much lower prices.
There are quite a few good factory direct manufacturers near you within a reasonable driving distance and I would put my efforts there rather than any chain stores or outlets that sell major brands in your area.
Post #2 here include the Connecticut options.
Post #4 here also has some options in southern Massachusetts which are close to you.
With lower back issues … good alignment becomes especially important which means avoiding comfort layers that are too thick and/or soft. This is especially true with memory foam which is a less supportive foam and if you go in this direction it would be wise to use high quality and thinner layers either by themselves or in combination with other materials such as latex.
You have some really good choices close to you 
Phoenix