Walt,
You are going in two different directions here. Flexible is what you want for a Fillet / Boning knife. These are usually thin.
A kick butt Combat knife that really usually gets used for opening crates, cutting rope, opening windows and maybe digging holes and possible someday fighting is a thick piece of steel more along the sharpened pry bar look these days. Flexible, 1/16" 3/32" thick. Combat 1/8"-3/8" or thicker.