We recently discovered the seller Crows Creek Customs on Etsy. They’ve been creating these high end, custom keepsake boxes for customers for a while. While each box consists of quality hardwoods and incorporate secret hinges, they also contain another secret.
Once opened, most of these boxes have a false bottom that can be removed to reveal a hidden storage compartment in the bottom.
Crows Creek has a number of these boxes listed, but it looks like they would make something to fit your custom requests if you wanted.