European larches, and western larches, and alpine larches all come from mountainous habitats. They like moisture levels similar to what keeps a spruce happy.
Larix laricina, the eastern NA larch, aka tamarack, is a bog creature in the southern half of its range, spreading into more general habitats in the northern reaches of Canada east of the Rocky Mountains. Eastern larch prefer moisture.
In the hottest couple weeks of summer, one could always set the pot in a tray of water, where the water level comes part way up the depth of the pot. Then as weather cools, you can remove the tray and treat the larch more like a normal spruce, meaning moist, not allowing to totally dry out.
I currently do not have any larches.
@crust is our BNut larch expert, though sometimes he is busy and does not check in often. Perhaps he will comment on potting media he uses and how wet or dry he allows his larches to get.
In the absence of a comment from Crust, I'd go with the 1:2 Akadama & pumice blend. Skip the lava, it holds less water than pumice. Or I would go 1:2 Orchiata bark & pumice.
If you really want to keep the soil wet, sift Canadian peat, only keep particles larger than 1/8 th inch, and blend some of that into your mix. But I would not go much over 20% peat, because peat causes problems when it gets too dry, it compacts, then does no re-expand after being wet. And peat breaks down, often in less than 2 years. Using peat requires more frequent repotting. Generally I quit using peat years ago, but I did use a 1:2:2 peat, bark, pumice blend for azalea. It would also work for blueberry.
But if I were you, use search engine to read everything Crust posted on BNut about larches, and do what he does.
I know Peter Chan of Herons Bonsai has a video on soil mixes and he adds some compost to his soil so they don't dry out so quick.
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