DIY Build question

Looking at going with the Combiz-zone springs, 2" talalay medium support layer and 2" talalay soft comfort layer.
I am a 180lb 6ā€™ mostly side sleeper, and prefer a rather firm mattress. Maybe because I feel they always end up softening up? I currently have a Casper from Costco, started out great but after 2 years offers no support for my back.

My question is what is the most ideal combination of latex layers? I noticed most of the mattresses only use one 3" layer. Iā€™m hoping the extra 1" will provide even more comfort? Would having 2 - 2" layers together compact against each other ok? Or would I still want at least a 3" top comfort layer over the 2" support layer? I was trying to keep the mattress to 12" or lower.

Also, since I"m stuck on latex thickness, is it ok to just order the components and no case? Then add a case layer after settling on size?

A mattress protector serves as an improvised cover.

I just ordered a mattress from Arizona Premium Mattress, after talking with the owner Ken. Everything they sell is effectively DIY, although the popular combinations are packaged. He gave solid advice.

Back in the sixties and seventies one saw bare foam mattresses all the time. People would smoke joints at parties on bare foam, unaware that at that time a generic foam mattress was roughly gasoline in solid form.

I think that is a solid choice and you can wait to get the cover. Many of our DIY customers go with either 2 2" layers or 2 3" layers. When you do add the cover it will put you just over 12" however.