The bed package is $2.50 per package, not per day (unless you want a new package each day). They hand it to you during check-in--you make the beds.
Here's some pictures of a Housekeeping Camp camp (click on "photo gallery"):
http://www.yosemitepark.com/Accommodati ... gCamp.aspx
It's been awhile since I stayed there--don't remember the matress firmness. It's usually freezing at night that time of year (although not yet), so I would bring extra blankets just in case. Bring warm clothes too.