It's always a risk running cohort units. However you've already got the right idea out of the start gate. Cohorts are best on the flanks and in small units. If you go too large they become unweildy and you relegate them to frontal combat. This is a bad plan because skinks do not belong in combat. Generally you'll loose greatly in combat resolution because of the amount of skinks you lose. Your only saving grace is if you have an uber large unit that maintains more ranks and therefor stubborn.
Using Life or Life will help the unit but you still have to deal with the skinks having virtually no save (usually a 6+ ward as their shield save is negated by str 4+) Giving them regeneration, higher toughness, and or bringing them back to life is all well and good but does little for combat effectiveness. Giving them ASF and higher initiative is nice for combat effectiveness but they still die in droves.
As I said at first. Small units on the flanks. 1 Krox and 10 Skinks, on the flank where attack backs are minimized. Good luck!