Just everything else I wash with in the shower: pine tar soap, a face wash, shampoo, then conditioner. Whiskers are so hydrated at this point, they practically explode off my face when touched by the edge.
It's also my understanding that alkali helps by breaking down sebum which is raised to the surface through the hair follicle. The hair is well protected by the sebum which acts as a moisture barrier. Properly breaking down the sebum assists in water ingress to the hair which makes it softer and easier to cut.
I know personally a good wash and a few minutes of hydration halve the shave effort required, though it doesn't tend to add to skin damage. However a long hot shower will cause my skin some grief. It's a balancing ask.Interesting theory, and makes perfect sense. I often wash with just water, and wonder if this is contributing to my blades not lasting longer in the Excaliber Club (waterproof stubble not getting thoroughly hydrated).
I can get up to 30 shaves already with the right blade, but this might make a further difference. However, I also don't tend to get irritation and rarely need to use alum or a balm, so maybe the sebum is protecting the skin too. I'll give this a whirl for a while (bar soap is the only other thing I use anyway) but if I start getting any redness, I'll got back to water only and shorter blade life.
I like to use a high glycerin bar soap or CVS Daily Facial Cleanser. Nothing fancy. I usually wash my face twice, just before shaving.