If you have an old Jenga set, you could just do what I did:
It's about 4 columns across for a 60% board, 5 columns for a TKL, and 6 for a full-sized board. Since I took this picture, I added another row, so it's 4 high and 4 across. Height feels exactly right to me. Run a single strip of duct tape underneath to keep them all together. Folds for travel
Been using this one for about 2 years now, I think.