Hi jmarkk1,
The thickness of a mattress isn’t nearly as important as the design of the mattress and the combination of materials that are inside it. There is also more about the most effective ways to choose a mattress (either online or locally) in post #2 here that can help you identify and minimize the risks involved with each of them but when you can’t test a mattress in person then the most reliable source of guidance will always be a knowledgeable and experienced manufacturer who can help "
talk you through" the different options they have available and will know much more about “matching” their different mattresses to different body type and sleeping styles than anyone else (including me).
Unfortunately this isn’t specific enough to be useful as a reference point for the type of mattress that you may do best with and Serta isn’t transparent about the quality of all the materials in most of their mattresses (see this article) and I would tend to avoid any of the mattresses made by the major manufacturers anyway (see the guidelines here). I don’t know of another manufacturer that makes a mattress that is specifically designed to be similar to any of the iComfort mattresses so the only way to compare another mattress to the one you liked would be a more subjective comparison based on your own personal testing and experience.
The mattress shopping tutorial includes two links to lists of the better online options I’m aware of (in the optional online step) and if you are in a lower budget range then post #3 here and the posts it links to includes some of the better lower budget online options I’m aware of as well.
If you let me know your city or zip code I’d also be happy to let you know about any of the better local options or possibilities I’m aware of.
There are also some guidelines in post #3 here and the posts it links to that will be helpful for those that are in higher weight ranges and with your weight I would also consider mattresses with higher quality/density materials if you are comfortable with a higher budget range or with different materials other than memory foam.
Phoenix