Memory foam mattress
We have the model with the pillow top + the low box. Currently the box + mattress are stacked on the floor. The height is comfortable for us and safe for the little one. I'd say he was able to crawl in and out of bed well by 1 yo. We've had the bed about 4 years.
The only big complaints I have with the bed are that it can get real warm from retaining body heat, and can become really hard if not slept in for a few days.
I have been co sleeping on memory foam mattress not tempurpedic but from essentia its supposed to be more natural without toxins or flame retardants. I never had problems with it and my DD has been sleeping on it since she was 4 months old w/o problems. Also if you have it on the floor make sure you get a coco rug mat or somekind of a frame for it so it doesn't get moldy.