This is from the sticky at the top of this forum
Dry Laundry Soap
by Simply Nurtured
2 cups castile soap flakes (you can grate a bar to get flakes)
1 cup washing soda
1 cup borax
3 - 6 drops essential or fragrance oil
Mix all ingredients, store in sealed container. Use 1/8 - 1/4 cup per load.
Recipe doubles fine.
I have used a formula similar to this and it works great even in my HE washer. The grated soap I used was Fels Naptha. Washing soda and Borax are both super cheap so that's great. Washing soda is different that Baking soda, just wanted you to know (you probably already do) to avoid the initial mistake I made.
From the internet
"Washing soda—sodium carbonate—is in the same family as baking soda. It has just been processed differently. It is much more caustic/alkaline, with a pH of 11, and while it doesn’t give off harmful fumes, you do need to wear gloves. It is found in the laundry section of most supermarkets. Arm & Hammer is one brand; Shop and Save has a generic house brand.
Washing soda cuts grease, cleans petroleum oil, removes wax or lipstick, and neutralizes odors in the same way that baking soda does. Don’t use it on fiberglass, aluminum or waxed floors—unless you intend to remove the wax."
Anyway, the DIY stuff I made worked well, but I have since switched to soap nuts which I love. I use them with a little borax and vinegar in the final rinse and my laundry comes out as clean as with detergent and smelling fresh, not perfumey. They are the best.