We bought my ds the convertible crib that lasts until age 12 with some basic add-ons.  Right now, he transitioned from the toddler bed and we're moving to the full size bed.  Here's the problem, the toddler bed used the same mattress as the crib, which we bought several years ago.  It was an organic mattress around $500-$600.  Now as I'm pricing the full size bed and mattress springs...it's about $1500!  My dh won't pay that much and so now I'm trying to find a cheaper,...