Hi beth819,
At your weight and height … I’d guess you’d be most comfortable with a comfort layer on the softer end of the typical 19 - 24 range. With your side and back sleeping and lighter weight … it’s likely that somewhere in the range of 2-3" would work well. This could be over an innerspring, polyfoam, or latex support core (with either one or multiple layers) depending on your budget or your preferred feel … as long as the pressure relief and alignment is good.
Latex also comes in a very wide range of firmness levels so it could be that the latex you tried would have been soft for someone else that was heavier but was too firm for you because lighter weights generally need softer foam. Of course … adding a little bit of memory foam either on top or under a thinner layer of latex can also be a very good choice which many people like a lot. Good quality memory foam is fine for those who like the feel (it’s very different from latex) and who are also OK with the way it reacts (it’s a warmer foam although some of the newer ones are cooler than they used to be and it also is more movement restricting than the more elastic and 'springy" latex).
Your own personal testing is the best way to know for certain so these are just some guidelines to give you a general idea of where to start.
Post #2 here includes some of the local manufacturers that are near the Ft Lauderdale area. The easiest way to get started and narrow down the list a bit is from home by calling some of them and letting them know a bit about your height and weight and your overall preferences and mattresses you have liked or are considering so they can make some suggestions about which mattresses they carry that would be worth including in your research. I would then pay a visit to the ones that sounded most promising and helpful. Most local manufacturers are very open and helpful on the phone and this can save you a lot of traveling time and help you know what to expect when you visit them.
You have some very good choices around you whether you end up with a latex, memory foam, or a combination with other materials. In most cases half the battle is finding the better outlets that are knowledgeable and open and committed to helping you make your best choices (which is one of the reasons I like local manufacturers). As long as you pay attention to what I call PPP (Pressure relief, Posture and alignment, and Preferences) … then there are many combinations which could work well for you for pressure relief and posture and the difference between them would boil down to which one had the best value and included the preferences and “feel” that were most important to you.
If anything … your biggest challenge may be choosing between some really good choices … all of which would likely be much better in terms of quality and value than most of the major brands (like the iComfort) and the mass market stores that tend to carry them.
Phoenix