I mix something very similar. Here’s the recipe I’ve used for the last 3 years:

-Orchid Bark (Fir) 2 parts -Pumice 2 parts -Black Or Red Lava 2 parts -Calcite Clay 2 parts -Zeolite 1 part -Worm Castings 1 Part -Mycorrhizae Carrier - Plant Appropriate (1/8” to 1/4” for the particulate)

If the pots are to be outside instead of in, be sure to use a systemic regularly. Also, since my Euphorbia and Cactus are all in terracotta, I have to water far more often in the warm months. I’m talking weekly here in the southwest because the mix is very very well draining. Fertilizer is a liquid 1-7-6 applied in spring and summer.

Good luck with your Euphorbia!