kmby,
Most if not all Serta mattresses are designed to be used on a firm non flexing foundation and a box spring wouldn’t be the best choice for a support system and may even void your warranty.
I would keep in mind that your needs and preferences now would be different from what they were as a child and that your mattress now which is the major part of your sleeping system (more important than the box spring) would also be very different from the mattress you had when you were a child and it’s the sleeping system as a whole that makes a difference … not just one part of it.
If you are looking for some additional “comfort” and pressure relief then a topper would probably be a better choice than a box spring.
Post #2 here and the topper guidelines it links to has more information that can help you use your sleeping experience on a mattress as a reference point and guideline to help you choose the type, thickness, and firmness for a topper that has the best chance of resolving any “symptoms” or discomfort you may be having (as long as they are related to needing more “comfort” or additional pressure relief).
Phoenix