I don' t know what the best material is, but I can show, how I protect my frosthardier citrus.

For younger plants, or plants with new grafts, I take
a double layer protection with inner layer oc cocos mat and
a second layer with frost protection fleece.
For good wrapping and space around the plants, that not so much leafes touch the protection layer, I put some bricks around the plant and put sticks of bambus in the holes of the bricks. Around bricks and sticks I wrap the layers and fix them with clamps. In the inner I still lay some water bottles.

For the Prag chimera, which grows slow and is hardy but still small, I used only one layer of frost protection fleece.