Hi Daubernurse,
It sounds like you made the best of a difficult situation and made the “best possible” choice with your circumstances.
If your mattress ends up being too firm then a topper can help with additional pressure relief and can also extend the useful life of the mattress. It also has the advantage of being replaceable if it softens or breaks down sooner than the mattress without having to replace the entire mattress.
If you do decide to go in this direction after sleeping on your new mattress by itself then the topper guidelines in post #2 here and the posts it links to may be helpful.
I’m glad the site was able to help … at least to some extent or as much as was possible in your circumstances.
Phoenix