We have an OEUF Rhea birch white crib for sale with a conversion kit. In the photos below we have the conversion piece on, but we still have the other side rail so it is easily turned back into a baby crib. 

You can read about both the crib and kit on the company listings: 

Or on the Amazon listings: 

We bought it about five years ago, but it’s still in great shape — a few little marks on the corners, but that’s about it; everything holds together perfectly. It comes from a smoke/pet free household. Asking $100 OBO. 

I don’t know if it’s that common to get a mattress second-hand, but if you buy the crib you’re welcome to our daughter's! It’s also five years old, but it’s still a really great mattress — firm and clean. It’s handmade by naturalmat, which you can read about here: 

They don’t seem to be producing our particular model anymore, but it’s this one: 

Hope these can find a home somewhere! Thank you! 

Benjamin