Hi I have been using this for more than 2 years now with no issues. I don’t know about sturdiness with conversion. I am sure company would have done all required test for convertible too. Not sure if my answer is helpful to you. Thank you
Pretty sure you attached the mattress support upside down. From the pictures online it looks like the brackets are supposed to attach to the crib above the rest of the mattress support, not bellow (so the mattress support "hangs" from the brackets, and aren't propped up above them like this). Glad to hear it's been working for you even like this though. :)