We are using the Z-flo fluidized positioners on our unit, but we are trying to put into place a protocol/criteria on which infants to use these on, since they are so expensive. Also, to keep our kiddos in them longer without risk of them being taken off them too soon (not everyone is in love with them and they toss them the first chance they get). Does anyone out there have a weight max or minimum, or certain criteria for use?? Which z-flo size do you use? Also, wondering what you use to cover it with. I've read some units use pillow cases just on top, like a draw sheet, others put them in pillow cases, some use the provided covers, some use regular blankets, what's the consensus?? One more thing... do you take out the giraffe bed mattress, or leave it in?? Thanks for your input!!