Call a company called LaJobi, they are the actual manufacturer not Graco. I guess graco just put their name on it to sell it. Good luck with that as they were not helpful when I called asking how to change it to a toddler bed .
Graco isn't out of business. And there is no conversion kit. You just take the front off the crib to make it a toddler day bed. And for it to be a full-sized headboard it connects to any standard metal bed frame.
I'm really not sure about that mattress model but the matress I used is 58 inches long and 29 inches wide so it's about 4 1/2 ft by 2 1/2 ft I'm pretty sure all crib matresses are relatively universal size. This crib is not an off size or extremely small we actually took the matress from another family members old crib and it fits perfect. I just don't know the name of the mattress, but this crib is really great quality, very sturdy, and pretty perfect for my daughters nursery. My wife loves it and she is really picky about name brand merchandise so that's saying a lot about this basic style crib