Finishing in Progress

So, finishing is in progress this weekend.  I was sort of dreading this--but once all the backstitching was done, the actual assembly has been going very smoothly.  I really like this sort of finishing actually.  As this is my first 'mattress' pincushion, I do have a question--what should I stuff it with?  I have lots of the sort of wispy stuff that goes into pillows and I have some quilt batting which is thicker.  I was wondering if anyone uses matte board inside to give it a little more structure and weight?  I contemplated using the stuff you iron onto the back of the linen as well, but I opted not to (as I would have to dig through bins to find the stuff).  Any suggestions?  I will hopefully finish it later this afternoon after I get chores out of the way, so any input is welcome.