Hi agims,
It is possible that your old mattress used fewer foam layers on top of the spring unit and used basic polyfoam layers, and while you “sunk into” it more, that could have been the result of loss of support (which you indicated improved on your new mattress) as opposed to being “insulated” with surrounding foam, which may be happening more on our new mattress. Additionally, your new mattress has some foam edge encasing which your old mattress may not have had, which can impact breathability. Also, the use of memory foam, which is less breathable, can be impacting your comfort.
I’m guessing that this mattress overall contains quite a bit more comfort material on top of the support unit as compared to your old mattress, and this is impacting your personal temperature preference.
Have you changed your mattress pad and sheets on this mattress as compared to your old mattress set? This can have a dramatic impact upon sleeping temperature, so be sure to read about that in the links I provided in my earlier reply.
There are some additional comments about wool toppers and a list of some of the better sources I’m aware of in post #3 here. I’m leery of some of the Amazon vendors, so be sure to check out the sources listed in that post. Wool certainly can assist in temperature regulation, although I tell people to attempt to solve the issue with the complete mattress first and not purchase something, if possible, that needs the addition of an extra product to achieve your desired result, unless there is a compelling reason to do so.
Phoenix