I've just discovered an ingenious idea!
Basically, my special blanket and the floor with padding. We were having the same problems and have been struggling with naps forever. This has been working recently.
My dh is a cover hog, so I have my own auxillary blanket that I use which is conviently covered in mama-stink. When dh falls asleep nursing (or in the morning if she's still out when I wake up), I put my blanket on the floor and lay her on it, kind of bunching it up around her so she feels secure. Right smack dab in the middle of her room (Even though she's not a roller) with some soft music on.
She actually slept for 2 straight hours the other day and I got work done! It was great!
It's worth a shot.