Hi Calpyro,
Congratulations on your new mattress 
As you know I think you made a great quality/value choice and I’m looking forward to finding out how you like it once you’ve received it and have had the chance to test it out for a while.
I would always make sure that you give any new mattress a few weeks before considering any changes so that the mattress has a chance to break in and you have the chance to adjust to a new sleeping surface that may be different than what your body is used to sleeping on (see post #3 here).
If after the first few weeks (generally 30 days is a good idea when possible) then if you find that the mattress is too firm for you then they have a great return policy if you decide to return the mattress and choose something softer. If you decide that you would prefer to add a topper and you just need some additional “comfort” and pressure relief then post #2 here and the topper guidelines it links to can help you use your sleeping experience as a reference point and guideline to help you choose the type, thickness, and firmness for a topper that has the least possible risk and the best chance for success and also includes a link to a list of some of the better online sources for toppers I’m aware of as well.
Phoenix