For inflatable pads, the type that have open cell foam in them so they auto inflate, I use the shorty pads. My feet and knees do not need that much padding. If I feel I need any more padding under my knees, a few articles of clothing under my sleeping bag works.

The pads that auto inflate do not have any problem with mold since they draw in atmospheric air. I usually blow in one more puff by mouth before I close the valve, but I have not had any problem with them.

I have been bringing an air mattress on cycle trips for the past three years instead of the auto inflate pads. The air mattress is thick enough you need full length, thus it is a bit heavier than the self inflating pads. But it packs down tiny so it is easy to get into my panniers. But, you have to inflate those, they are not auto-inflate. I prefer the REI Flash model air mattress, it has two large valves, an inflation and deflation valve. It is easy to get the air out to roll it up. Other pads that have a single small diameter valve are harder to pack up in the morning.

A friend of mine has a tiny little air pump for his Thermarest air mattress, I think it takes AAA batteries. That is one way to reduce moisture from getting into your air mattress. Thermarest made the pump.
https://www.backcountry.com/therm-a-...oair-mini-pump