I have been using 50% lard, 50% coconut with a 3% lye discount. (Maybe when I get more confidence and experience, I'll try a lower discount.) I have done stovetop HP and CPOP. A day or so after the soap is made -- while it's still soft -- I shred it with my food processor, then roughly mix the shreds with equal parts by weight of baking soda, borax, and washing soda.
I use the blade in my food processor to powder the grated soap with the other ingredients until the soap is a powder -- the texture I'm going for is like coarse cornmeal. I include the other ingredients with the soap in the processor bowl to keep the soap from softening and "mooshing" together rather than turning into a powder. (Found that tip out the hard way.)
I use about 2 tablespoons of this mix for a typical medium load and 3 tablespoons for a dirty or large load. I have a top loading HE washer, and I almost always use cold water. Because the soap is so finely ground, I haven't had any problems with it dissolving quickly and rinsing out properly.
I got curious about the other ingredients -- what do they contribute to the party? You'll find recipes that do have baking soda, and others that don't, for example. Given the many variations on this theme, it's obvious that there are many opinions about what makes a good laundry soap mix. Here's what I concluded:
Baking powder is a fabric softener, secondary water softener, and pH buffer. Its pH is slightly above 7.
Borax whitens, cleans, and deodorizes. Its pH is about 9.5.
Washing soda is the primary water softener. It whitens and degreases. Its ph is about 11.
A lot of people, like Siefenblasen, also add oxiclean to the mix. I have seen some recipes that include the citric acid that Lindy mentioned, but not as many. I add oxiclean separately as needed -- that's just my preference.
Oh, and I stumbled across some inexpensive plastic shot glasses at Walmart -- a dozen for under $2. A shot is about 2 TBL, so they make great scoops and reduce the temptation to add too much soap to the load. A little condiment cup scrounged from the local burger joint would work too.
Pet peeve -- I hate the big caps that commercial laundry detergent comes in!!! I am convinced they are cleverly designed to make the consumer use way too much expensive detergent. :x