If you want a laser, thinking something like 7 degrees per side and .010" or less behind the edge and really thin at the spine, then you need a low carbide, very tough, very hard steel. White steel isn't bad. In the US you can find a number of equivalents. 52100, etc.
Finding a maker who specializes in super fine grained, super hard steels is tough outside of kitchen knives. But you're right, that kind of steel would serve very well with leather.
Chris mentioned a maker who is doing exactly what it is you're wanting. Bluntcut makes working scalpels using steels that can be taken super thin and super hard while retaining more than adequate toughness by minimizing grain size. The hardness you need increases sharpening time but also increases the amount of work you can do between sharpening. With them being so thin it doesn't take long to sharpen anyway.
As far as steeling goes, no need for that with hard steels. Steeling is for soft steels that roll and deform easily. All you'd need is a small diamond rod or plate to run across the edge every once in awhile. With a knife being .010" or less behind the edge and a thin spine you don't really even need a razor sharp knife as the thin geometry is what's doing the cutting. The sharp edge is really to make the initial cut. Everything after that is just the blade geometry. The thinner the knife the less pressure needed to make the initial cut which helps prolong the edge as well.
That kind of knife wouldn't do as well with, say, dirty, hairy hides but clean leather it'd most likely be pretty amazing.
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