Tree fern fiber can be replaced with fir bark. You can use orchid potting mix in replacement of orchid bark.
Peat moss brands vary, just avoid any that have fertilizers in them.
Other soils have been tried and failed. Potting soils compact and restrict drainage. Some hydroponics soils drain well, but had added items like vermiculite and perlite in them, which even small frogs can ingest and become impacted.
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