Sheet protectors for cradle & crib

Cathyr1003

Hi ladies!  I am due in February and was hoping you could help.  I have seen sheet protectors in babies r us.  I am thinking this would be super helpful so i dont have to constantly change the sheets on cradle & crib mattress.  Plus my crib mattress is super heavy & the sheet is very tight.  I cant imagine having to change constantly.  Has anyone used these?  Also, are they safe for cradle as well?  I want to be very careful with putting anything inside the crib/cradle (sids).  Thanks in advance!!