Hi mikes425,
While it’s not always possible to to track down temperature regulation issues for any particular person on a specific mattress because there are so many variables involved (including your room temperature and humidity, your bedding and bedclothes, and where you are in the “oven to iceberg” range) and some people can sleep warmer on mattresses that most people are generally fine with … there is more about tracking down a potential cause or causes for temperature regulation issues (at least to the degree possible for a specific mattress) in post #2 here and the posts it links to that may be helpful.
Softer foam materials that allow you to sink into the mattress more deeply along with some types of mattress protectors or encasements (especially the ones that have a semi breathable waterproof membrane) can both affect sleeping temperature … especially for those that are more towards the oven end of the “oven to iceberg” range.
A tight mattress protector or encasement that creates a “drum effect” can also affect the feel of the mattress underneath it.
The deeper support layers of a mattress (such as an innerspring) generally have less effect on the sleeping microclimate and temperature regulation than the layers and materials that are closer to your skin.
Most back sleepers also tend to need and prefer slightly firmer mattresses than side sleepers (who generally need softer comfort layers to relieve pressure points than other sleeping positions).
Phoenix