Thankfully a crib and a toddler bed mattress are the same size, so whether it is in the crib or on the toddler bed frame, you have the same size area to cover. Finding the perfect bedding can be a bit more tricky though.
I found some great sheet sets online for toddler beds that I use on both my crib and my toddler bed (I have a daughter in each, they share a room and I wanted them to have matching bedding).
Before I redecorated their room and went Ikea crazy I made their blankets or bought some adult throws/toddler throws. I still make blankets to go under their top comforter set, and they enjoy knowing it is their special blanket from mommy. You can also look online for toddler bedding. It should fit your crib also. The main difference is that the crib has taller rails than a toddler bed.
Hope you find what you are looking for :)