Best substrate for Cushion moss propagation?

I’m wanting to create a box of cushion moss to continually grow.

I have a suitable plastic box and a grow light setup (if that’s not the best way I’m happy to change) but I can’t find an answer to what the best substrate is.

I’ve seen just sphagnum moss substrates tend to be good, seen peat moss is good or maybe a mix of both?

Would love to hear from someone with experience as to what they think the best substrate is.