Hi mraND,
If your mattress has no soft spots or impressions and your main goal is to make the top layers softer and improve pressure relief then a topper can be a good solution. Adding a topper to memory foam that can increase airflow and cooling though can also present some challenges though because it will reduce the amount of heat reaching the memory foam which can make the memory foam firmer … especially if it is more temperature sensitive like the Tempurpedic.
The topper guidelines in post #2 here and the other posts it links to can help you make the best possible topper choice. It also links to sources for memory foam, latex, polyfoam, and wool toppers.
Wool is a great choice for temperature regulation but it will also compress with time and gets firmer and isn’t as soft or pressure relieving as foam toppers. It’s great for the “feel” of a mattress and to improve temperature regulation and can add some localized cushioning under specific pressure points but in terms of overall pressure relief and softness it wouldn’t be as effective as softer foam materials. It would probably be a better choice over more resilient and less temperature sensitive materials. You can read a little more about the different types of softness in post #15 here.
Overall … I would be quite cautious about adding thicker layers of wool over more temperature sensitive memory foams like the Tempurpedic 5.3 lb memory foam because while it will add some “surface softness” … it will also likely firm up the memory foam below it and you would run the risk of ending up with a firmer mattress than you currently have.
The link to wool toppers in the component post includes more information about the snugfleece wool toppers and Christian at Biosleepconcept is very knowledgeable about the products he sells and would be well worth talking to about the BioSleep topper as well (see post #34 here) although I would lean towards either a softer latex or a memory foam topper on top of your Tempurpedic.
Phoenix