Hi bbel,
I’m not quite clear what you mean here but they only have 4 firmness levels for each layer XF - F - M - S. There aren’t any “subdivisions” of each level.
I would be cautious as well. All the combinations you are considering would be very firm and outside the range that would be comfortable or work well for most people … especially if they are an average build and side sleepers. I would also keep in mind that a mattress that is too firm can be just as unsupportive as a mattress that is too soft. If you sleep on the floor for example there is very little to no support under the recessed parts of your body such as the small of your back on your back or the waist when you are on your side.
When you can’t test a specific combination in person then the best approach is always a more detailed conversation with the manufacturer so you can talk through the pros and cons of your layer choices in more detail (see mattress firmness/comfort levels in post #2 here). They have more knowledge and experience with their own mattresses and helping their customers match their body type, sleeping style, and preferences than anyone else and are in the best position to help you make the best possible choices. They also offer split layers so each of you can choose different layers for your side of the mattress and they also have a good layer exchange policy just in case you need to make any changes after a purchase based on your actual sleeping experience.
Phoenix