Hi guys,
I’m currently designing a sauna. An issue that keeps stumping me is the floor. I want it to be made out of wood and I want to use a subfloor so it feels solid. My thinking is 2×6 joists- vapor permeable barrier- mineral wool- plywood subfloor (possibly acts as a vapor barrier?)- underlayment (cork)- finished cedar floor (1×4).

It’s been recommended that I do joists- ff-pir(insulation & vapor barrier)- air gap- finished wood floor. 

My hesitation with not using subfloor is that when you walk (or jump who knows)  on the floor it will feel weak.

Can anyone offer insight into how I can make a strong, air tight, wood floor that will last decades. Thank you!