Hi BmoreE,
It’s unfortunate that your wife doesn’t like your mattress as much as you do and it seems that your original concerns about temperature didn’t turn out to be as important as the movement restriction that can be part of the characteristics of mattresses that use slow recovery materials like memory foam.
In any case … post #2 here has more information that may be helpful if you are considering mattress surgery as a “last resort option”.
It may be worth considering just removing half of the memory foam layers (or even just the top 3" memory foam layer) on her side of the mattress and replacing them with a faster response material with the same thickness so that you don’t have to cut the whole mattress in half and can use the same base materials. I would probably try just replacing her half of the top 3" layer and then you can always replace the deeper 2" layer as well if you need to later on.
You may need to be work cautiously if the layers are glued together and if you are careful you may be able to use the same cover.
If you do decide to sell it then you would meet the forum rules about selling a mattress and you are welcome to start a new “for sale” topic if you wish to.
Phoenix