This worked well, but as we settled in, we realized that more storage would be needed. I went through several design options with my shop supervisor and we decided on a simple pair of frames with deep drawers.
Using 3/4" plywood cut into ~24" widths at the lumberyard (two from each 4x8 sheet of plywood), we cut two boards to length for each side of our bed, then three dividers and two ends from ~16" widths (three from each sheet). We used L brackets to hold the frames together and to support each of the interior dividers. These guys were heavy just as boards, so when the frames were built, they were solid. They lived in the "walkway" of our room for about a week while we plotted the next step.
The support system Alex had built on the original bed included a 2x4 frame, similar to an interior wall. The 2x4s were covered by 1x8 boards, and the legs were made out of additional appearance boards of narrower widths. We decided to reuse some of the previous materials in building the frame for the center of the drawers. Two of the boards were cut down to the length of the frame and anchored to the backs of the dividers and end frames, ~ 1-1/2" below the top surface. Additional boards were cut down to the right length for our mattress to fit across on top of the "slats" resting on the ledger boards. At the head and foot, the slats were secured into the two sides for safety.
We found that the drawer frames could be used as cubbies while the drawers and trim pieces were addressed. Andy and I cut down some underlayment, previously used on the slatted frame, to use as backing for the drawer cubbies, and I crawled under and hammered them in.
This winter when we pulled out our warmer clothes and outerwear, I strategized putting summer things away under the bed as we only need to access those twice a year for the changeover and it should be as easy as possible instead of my ear warmers being MIA into November... The clear bins we use for clothing storage fit under the bed with a little breathing room, and I also stashed our summer comforter and pillows in space bags there as well near the opening for easier access.