Yes, losing the 4” box spring is a good option (just be aware it may make it harder to tuck in the sheets bc of the side rails). You may also want to investigate how the bottom feet are attached to the bed posts. It may be possible to remove them without causing any damage and either leave them off or replace with a shorter option.

@beesneeds, we have a brand new high end mattress that is the bee's knees and all that. I've reached out to Leonards of New england and they suggested a few things. Removing the center board and adding three horizontal slats with feet then I would drop a thick ply wood atop that and center the mattress. She even said some folks set a metal bed frame down inside!

Get a much shorter box base. They don't do anything except add height. You could remove it altogether and put your mattress on a sheet of plywood.

Lovely bedframe. What did you end up doing?

As a dealer who used to sell these beds, many of them, the easy way is to simply take off one of the "L" brackets and go to a local Blacksmith near you and have him replicate a set of brackets adding the additional drop that you want. You have (12) brackets tolal, expect to pay about $ 20 to $ 25 per bracket.

The issue though, is the middle support board that runs from head to foot.

You are fitting the longer drop brackets to that piece as well. Most of Leonard's beds were made by Stephen Plaud in Tiverton RI. Stephen has retired and sold his business to Scott James. You can call them and tell them what you want in bracket drops and they can supply you as well.

https://scottjamesfurniture.com/scott-james-furniture-blogs/tag/stephen+plaud