Help me plan my DIY wood stove water heater

[Mukiwa]

We are building a house with an insulated and hydronicly heated concrete slab as our floor and heat source. It will be heated with a propane boiler but I want to be able to hook it up to my woodstove in the future. Unfortunately the woodstove is not located beside the mechanical room so I have to run water line through the slab from the woodstove to the mechanical room. I will not be hooking up right away but I have to have the pipe in the slab before because once we pour the concrete I won’t have access to install a pipe later (obviously). What type of pipe should be used in the slab?

A few options:

Pex - I’m worried pex will melt with the heat of the woodstove,
Steel - I don’t really want to have threaded fittings where I can’t access them if they start leaking or something
Copper - $$$$$$

What would you use? And what size should the pipe be?