Fallgold

I extended my Raspberry bed today. My bed now has 8 more canes of Autumn Raspberries. These are Fallgold that produce yellow fruits They should start fruiting around the end of July. All i need to do now is cut down the canes to the second bud in a few weeks time once they have settled in; Ill do that when i mulch the bed.
Im still undecided what to use as a mulch-straw,manure,bark-chip!
I had read somewhere that you should not use mushroom compost on Raspberries and im toying with the idea of putting some cardboard down and covering with soil. Cardboard would be the cheapest (free)option!