Hi there CatZombie. I know some members here do not like the tortoise-specific substrates.
I used topsoil for a long time indoors but I switched to coir which I buy from these people:
https://www.fertilefibre.com/
When my tortoises are indoors they live in an upstairs room and topsoil is very heavy. Coir is light until the water is added to it so I add water to the coir after I have put in on the table. This way I am not carrying heavy topsoil upstairs and heaving it up onto a tiered tortoise table.
But I like the coir anyway. It's clean and cheap and can be put on borders in the garden when it's replaced.