You can find a large variety of beds and mattresses on the market. With metal bunk beds, both the frame and the ladder are constructed of metal.
Now that you each have enough room to get a good night's sleep, you will want to select a mattress that provides both of you with the support and firmness you need. If there was one complaint against the original mattress it was that it was a little on the firm side. This way, your child can enjoy the new bed, even if you don't think they're quite ready for the experience of sleeping in the top bunk.
Remember, when your purchase things online, you have to factor in shipping costs. Patients suffering from degenerative spondylolisthesis do benefit from an inclined bed with support under the knees. Building your bunk bed also provides the ability for customization.
There are king, full and queen size air bed models and even a style that will convert into a couch during the day. The best indicator of whether your child is ready for a bunk bed is if your child is able to safely navigate the bunk bed's ladder.