Hi SouthFL,
One of the tradeoffs of using a thicker wool topper on a memory foam mattress is that memory foam is temperature sensitive and while it can certainly improve sleeping temperature … it can also have a significant effect on the temperature response of the memory foam and can make a significant difference in the feel and response of the memory foam.
In many cases changing the type of mattress protector you use or the type of sheets and bedding that you use on a memory foam mattress will be “enough” to sleep cooler. There is more about the different types of mattress protectors in post #89 here and the posts it links to and there is more about sheets in post #7 here and the other posts and topics it links to.
Having said that … if you are exchanging your mattress for a mattress that doesn’t use memory foam in the top layers then your wool topper may still make a great addition to your mattress.
The Mary Beth Luxury Firm still has about 4" of unknown and likely lower quality polyfoam in the comfort layers which would still be a weak link in the mattress and I believe that it’s also a lower price than the Optimum Radiance so you would end up losing the extra you paid for the Radiance (or using it as a store credit depending on their policy). If you are exchanging for a mattress that will work for you without the addition of a topper then the “best” plan (outside of choosing a mattress/topper combination) is to choose one that has the least possible amount of unknown or lower quality materials in the top 5" - 6" of the mattress.
The Vinyasa is “on the edge” in terms of the amount of lower quality materials (2") but of course the tradeoff is that it’s in a much higher price range and you would need to spend a lot more money with your exchange for a mattress that is probably not a great value choice either (compared to other similar mattresses) even though the “weak link” is a little less.
If I was in your shoes I would probably try changing your mattress protector and/or sheets to see if you can “fix” the mattress without an exchange and then only do an exchange if the other options you have don’t solve the issues you need to “fix” (assuming there is still enough time in your 90 day exchange period).
Phoenix